The concept of guerrilla marketing subsumes a set of different innovative advertising instruments which aim at gaining a large effect with a small budget. Although these instruments are more and more often applied by practitioners, there is barely scientific discussion about the concept. Therefore, this study describes the evolution of the current understanding of guerrilla marketing as an attempt of gaining the attention of a large number of recipients at relatively low costs by means of a surprise effect and a diffusion effect. The study highlights how different guerrilla instruments (ambient, sensation, viral, buzz and ambush marketing), try to evoke these effects. Finally, since there is rare empirical evidence about the efficacy of guerrilla marketing, the paper outlines a conceptual framework and several propositions for further research from consumer behavior perspective and managerial perspective.

INTRODUCTION

In 1960, Ernesto Che Guevara, the leader of Cuban Revolution, described the Guerrilla tactic in his well-known book “Guerrilla Warfare” as a method of warfare that builds on raids and ambush attacks (Guevara, 1960). Marketers have adapted the concept to the business context during the 1960s as a means of gaining large effects at low expenses (Baltes and Leibing, 2008). Particularly during the last years, the popularity of the guerrilla concept has steadily been growing, because the effectiveness of classical advertising has been declining dramatically due to the following two reasons (Van den Putte, 2009). First, the average US-consumer is exposed to approximately 3,000 advertising messages in only one day (Kimmel, 2005). Facing this permanent flooding of attempts of persuasion, many people feel constricted in their freedom to make independent consumption decisions (Kalliny and Gentry, 2010). To reduce this psychological reactance, they try to avoid being exposed to and being influenced by advertisements (Edwards et al., 2002; Lessne and Notarantonio, 1988). Second, by confronting consumers repeatedly with the same type of advertisements they become familiar with these measures which cause a wearout effect (Bass et al., 2007). For that reason, particularly classical types of advertising lose their power to attract consumers’ attention (Balasubramanian et al., 2006; Darke and Ritchie, 2007).

To win the competition for attention, many marketers promote their products more aggressively by using more and more advertising activities (Alsamydai et al., 2010). This attempt, however, appears counterproductive, because it requires a higher advertising budget and, most importantly, it prompts even stronger avoidance behavior and wearout effects (Mburu and Mogorosi, 2003). In order to find a way out of this closed loop, marketers have to develop alternative concepts for attracting consumers’ attention without causing reactance (Al-Marwai and Jayashree, 2010). Several different unconventional advertising instruments have evolved (i.e., using unusual locations for advertising) which promise to generate a big outcome with small financial effort (Levinson, 1984). These instruments are subsumed under the umbrella of the guerrilla concept. It remains nebulous, however, whether guerrilla marketing is a unique concept or just an attractive name for a diffuse set of heterogeneous instruments. Due to the imprecise concept notation, it is still under-researched whether guerrilla marketing is an effective tool of communication and persuasion.

So far, some academics have already referred to the concept of guerrilla marketing when examining different instruments, such as buzz marketing (Notarantonio and Quigley Jr., 2009; Siefert et al., 2009), viral marketing (Van der Lans et al., 2010) or ambush marketing (McKelvey and Grady, 2008). Even in published papers authors use the term guerrilla as subject term (Moor et al. 2010; Van Wood et al., 2010). But the literature still lacks a scientific contribution which directly focuses on the guerrilla concept.

Therefore, the main purpose of this study is to stimulate the academic discussion about the guerrilla method in marketing and its related instruments. First, based on a short review of the evolution of the concept, we suggest an up-to-date definition. Second, we explain the main characteristics of the guerrilla concept which are a surprise effect, a diffusion effect and a low cost effect. We point out the level different guerrilla instruments are able to achieve in these effects. Third, as there is almost no empirical research on the effectiveness of guerrilla campaigns and on the managerial process. Thus, we suggest a conceptual framework and an agenda for further research.

THE NATURE OF GUERRILLA MARKETING

Development of the concept: The concept of guerrilla marketing has been changing during the last five decades. In the 1960s, many small and medium sized enterprises (SME) in the US were urged to find innovative ways of effective advertising with little marketing budgets. They attempted to equalize their size-related disadvantages compared to large companies by means of unconventional ways of advertising which they adjusted fast and flexibly to changing market conditions (Levinson, 1984). At that time, these guerrilla instruments were considered revolutionary because they were substantially different to classical advertising. As consumers did not inevitably recognize guerrilla activities as advertisement, they belong to the so called “below the line”-measures (Carter, 2003; Kimmel, 2005).

The concept reached wide popularity after Levinson (1984) had published the first comprehensive book on guerrilla marketing which provided guidelines for small businesses. The book appeared during the corporate crisis in the US, when the competitive situation had become tough because of numerous foundations of SME. The new strategy “small budget, big results” claimed to help SME surviving the crisis by means of innovative advertising activities. Ries and Trout (1986) outlined success drivers of guerrilla marketing (e.g., flexibility) which triggered a boom of guerrilla campaigns. At this time, marketers still applied the guerrilla tactic mainly to weaken their competitors (competitor oriented guerrilla approach; e.g., Levinson, 1984). During the subsequent decades, the marketing discipline has become more and more customer-oriented. The development of guerrilla marketing reflects this trend. The former objective has steadily been replaced by the goal of winning new customers (Solomon et al., 2009).

The changing nature of the guerrilla concept from a competitor oriented approach to a customer oriented approach is accompanied by a second development. In the beginning, especially SME applied the guerrilla approach. Now-a-days, more and more large companies are interested in this way of advertising. Due to global developments, such as the financial crises, they have to cut their advertising budgets. Hence, marketers put more emphasize on the performance of advertising activities when planning their campaigns (Kim et al., 2001). As a result, several different concepts have recently evolved which claim to fulfill the guerrilla principle of gaining big result at low expenses (Levinson, 2007). Advertising agencies which are not bounded to strict academic definitions and which need to sell innovative concepts, created different terms for the concepts, such as renegade marketing, covert marketing, diffusion marketing, under-the-radar marketing or vanguard marketing (Egan, 2007; McAllister and Turow, 2002). Nonetheless, all of these concepts are basically guerrilla marketing. Further, marketers developed several specific instruments which are applied under the roof of guerrilla marketing, such as ambush marketing, ambient marketing, sensation marketing, buzz marketing or viral marketing (Carter, 2003; Notarantonio and Quigley Jr., 2009; Hutter and Hoffmann, 2011a). To sum up, to date, guerrilla marketing is mainly defined by the vague objective of gaining big results at low expenses and an enumerative list of instruments. Literature lacks a clear explicative definition which provides clear criteria whether or not an instrument belongs to the guerrilla concept.

An up-to-date definition: Levinson claims (1984) all kinds of innovative and eye-catching advertisements belong to the concept of guerrilla marketing. Accordingly, guerrilla marketing is described as being fancy, atypical, unusual, original, provoking, flexible, dynamic, innovative and creative. Some authors stresses on the cost-cutting elements of guerrilla campaigns. Ries and Trout (1986), for example, recommend marketers to save costs by identifying market niches, creating a flat organizational structure and acting highly flexible. Despite different foci, all definitions of guerrilla marketing agree that the concept provides a solution of how to succeed in the competition for consumers’ attention and of how to avoid high costs for advertising campaigns. However, there are several different suggestions on how to achieve these objectives.

For the sake of clarity and in order to stimulate further research, this study proposes a more concise explicative definition. Obviously, a central characteristic of the guerrilla concept is the objective of an advantageous relationship of advertising expenses and effects. In the following, we will use the term “guerrilla effect” to describe the favorable ratio of cost and benefits. In this regard, we consider costs as monetary expenditures for advertising campaigns. The benefits of guerrilla actions are first and foremost an increase in consumers’ attention. To evaluate a guerrilla campaign, several additional criteria (e.g., improvement of image and sales figures) need to be considered. As discussed below, these criteria are strongly affected by the increase of consumers’ attention. Therefore, we focus on the basic guerrilla effect which is measured in terms of consumers’ attention.

The ratio of costs and benefits can be improved by intensifying the potency for drawing the attention of the audience to the advertising message. To achieve this goal, guerrilla campaigns try to evoke a surprise effect (Hutter and Hofmann, 2011b). In order to dumbfound people, guerrilla campaigns need to be new and unconventional.

Fig. 1:	The basic guerrilla effect

Moreover, to accomplish an efficient ratio, a relatively large number of recipients have to be exposed to a guerrilla campaign. Therefore, guerrilla campaigns build on a diffusion effect which is realized in an interpersonal or a medial way. Guerrilla campaigns are designed to stimulate consumers and/or the media to spread the advertising message. The more people addressed, the higher the aggregated surprise effect and, thus, the lower the relative costs per person of the campaign (= cost effect) (Fig. 1). Additionally, a low cost effect can be achieved by planning campaigns that require little expenses (e.g., by acting very flexibly to take opportunities of advertising at low costs). Summarizing, the present study deduces the following definition of guerrilla marketing:

Guerrilla marketing is an umbrella term for unconventional advertisement campaigns which aim at drawing the attention of a large number of recipients to the advertising message at comparatively little costs by evoking a surprise effect and a diffusion effect. In this way, guerrilla marketing campaigns are highly efficient in terms of the ratio of costs and benefits.

DRIVERS OF THE BASIC GUERRILLA EFFECT AND CORRESPONDING INSTRUMENTS

In the following, we explain in more detail the surprise effect, the diffusion effect and the low cost effect. We demonstrate how different guerrilla instruments try to evoke these effects. Although each guerrilla instrument consists of all three effects, some instruments are primarily applied to maximize the surprise effect, some instruments are explicitly designed to stimulate a diffusion effect and some instruments mainly aim at cutting advertising costs. To provide a categorization, we ascribe different guerrilla instruments to those effects they are mainly focusing at (Table 1). Note that this categorization is a simplification which highlights the effect that the instrument mainly addresses. The core of viral marketing, for instance, is to stimulate a diffusion effect. Still, it includes the other two effects. It builds on a surprise effect to make the message worth telling and, thus, to gain the attention of a high number of recipients. The fact that consumers themselves diffuse the message within their social networks saves advertising costs.

Surprise effect
Rationale: The core principle of the guerrilla approach is to surprise consumers with unexpected activities in order to draw their attention to the advertising message. Surprise is a result of the divergence of perceptions and expectations. Based on previous experiences, individuals develop schemas and thus expectancies about certain events (Rumelhart, 1984). According to the schema congruity theory (Mandler, 1982), the discrepancy between a stimulus (e.g., unconventional advertisements) and a schema (e.g., not expecting advertising messages at a certain place) can evoke surprise (Alden et al., 2000) (path 1 in Fig. 1). Unusual stimuli are processed more deeply than those that are considered commonplace (Waddill and McDaniel, 1998).

Table 1:	Surprise, diffusion and low cost effects and corresponding instruments

If expectancies are disconfirmed and the degree of disconfirmation passes a certain threshold, the resulting emotional reaction is surprise (Meyer et al., 1991; Stiensmeier-Pelster et al., 1995; Vanhamme, 2000). Surprise leads to a change in the cognitive activation. According to activation theory (Lindsley, 1951), a surprised individual suspends his previous activity and focuses his attention on the surprising event (Derbaix and Vanhamme, 2003; Meyer and Niepel, 1994) (path 2 in Fig. 1).

Advertisers can use different methods to surprise consumers, such as absurdity (Arias-Bolzmann et al., 2000; Dahlen et al., 2005), humor (Eisend, 2009; Schwarz and Hoffmann, 2009; Voss, 2009) and shocking messages (Ay et al., 2010; Dahl et al., 2003). Another possibility to evoke surprise is to implement advertisements in atypical locations applying atypical media and means of promotion. For example, light projection onto famous landmarks, huge poster-like messages on building sites or giant representatives of products contradict consumers’ expectations. Consumers, who are surprised by these unexpected advertisements, can hardly avoid processing the advertising message (Johnston and Hawley, 1994). In this way, the surprise effect helps to attract the attention of consumers who try to obviate being exposed to advertisements (path 3 in Fig. 1).

Instruments: Ambient marketing and sensation marketing are instruments that explicitly try to surprise consumers by placing advertisements at locations where consumers do not expect them. Ambient marketing is the guerrilla variant of classical outdoor advertising. Advertisements are placed at unusual locations in the direct social environment of the target group (Krautsack, 2008; Moor, 2003). Luxton and Drummond (2000) defined ambient marketing as “placement of advertising in unusual and unexpected places (location) often with unconventional methods (execution) and being first or only ad execution to do so (temporal)”. According to Barnes (1999), the distinctive feature of ambient advertising is to surprise consumers by confronting them with incongruous stimuli in an uncommon background. Ambient marketing provides a wide spectrum of opportunities ranging from low cost fly posting stickers and graffiti proofs to advertisements in public bathrooms. Often gigantic (e.g., rebuild the airport baggage reclaim as a roulette wheel to promote a casino) or minimalistic (e.g., put a 50 inch tall fuel dispenser next to an original one to symbolize minimal consumption of gas) objects are presented. Ambient media is one of the fastest growing marketing sectors and due to its relatively low costs and the great number of targets reached its expected that the diffusion will take place rapidly (Shankar and Horton, 1999; Turk et al., 2006).

Sensation marketing aims at surprising pedestrians in public places by actions that go beyond the scope of familiarity (Hutter and Hoffmann, 2011a). Passersby look at a specific action, because it is unconventional and spectacular (e.g., actors performing a play in front of the theatre to attract pedestrians’ attention to the theatre). Flash mobs are a subtype of sensation marketing which is more and more often used. Non-commercial flash mobs consist of a group of anonymous individuals, who meet apparently inexplicably at a public place for performing a pointless action which lasts only a few minutes (White, 2006). Marketers have adapted the concept and developed commercial flash mobs in order to surprise passersby and to direct their attention to an advertising message. Ambient and sensation marketing have in common that both dumbfound consumers in their familiar environments. While ambient marketing includes installations for a specific time, sensation marketing consists of irreproducible one-time actions. For that reason, sensation marketing is also called hit and run action.

Diffusion effect
Rationale: In classical advertising, the number of recipients often determines the price of a campaign to a large degree (e.g., cost-per-thousand for advertisements in TV, radio or print media). Guerrilla marketing provides ways of increasing the number of individuals exposed to the advertising without increasing the cost of a campaign. Therefore, the diffusion of the advertising message needs to be stimulated in a goal-oriented and economic way (Solomon et al., 2009). Marketing literature has widely described how ideas and innovations diffuse among social networks and why consumers voluntarily forward a message (Bass, 1969; Gatignon and Robertson, 1991; Hoffmann and Soyez, 2010; Rogers, 2003). Particularly consumers, who feel strong emotions, are motivated to share their experiences (Rime et al., 1992). Consequently, to stimulate the diffusion of a message, advertisements need to evoke emotions (Menon, 2010). Guerrilla marketing explicitly attempts to trigger the emotion surprise. Surprised recipients are likely to talk about their experiences to other persons. In addition to stimulating a diffusion process, this word-of-mouth-communication (WoM) has another advantage over classical advertisements: Since friends are considered more credible than anonymous persons or commercial communication, WoM messages are highly persuasive (Arora, 2007; Herr et al., 1991; Smith et al., 2007). Because of this diffusion effect the attention of numerous recipients will be directed to the surprising message and to the brand (path 4 in Fig. 1).

Instruments: Viral marketing, buzz marketing and guerrilla PR are instruments that explicitly try to stimulate the diffusion effect. Viral marketing comprises different methods to initiate a communication process which spreads like a virus among potential customers (Ferguson, 2008; Phelps et al., 2004; Putrevu and Lord, 2003; Southgate, 2010; Woerndl et al., 2008). Marketers can trigger the diffusion of a message either in direct communication addressing multipliers that forward the message to other consumers or in indirect communication via different media. Stimulated by innovation in information and communication technologies, many new techniques of viral marketing have evolved during the last years. Video clips which diffused throughout the World Wide Web, are the most frequently applied method of viral marketing (Haque et al., 2006). As the advertising message is embedded in a video clip with informative, unconventional, humorous, sexual, or taboo-breaking content, consumers are motivated to forward the clip to their friends. In this way, video clips are a moderate priced alternative to classical TV-spots.

Buzz marketing is a precursor of WoM which has become more and more widespread, because it is very effective without requiring intensive spending (Mohr, 2007). Ahuja et al. (2007) defined buzz as “a multi-dimensional communication process that involves sending persuasive messages out via buzz agents (senders) to buzz targets (receivers) in the form of WOM (offline and online) conversations and retrieving market research information from buzz agents on the particulars of these buzz marketing experiences”. Accordingly, buzz marketing uses consumers as market researchers, advertisers, distributors and influencers in the decision-making process of other consumers. Marketers foster the referencing behavior of buzz agents by providing them with product samples, insider information and other incentives. To be persuasive, buzz agents need to match the characteristics of the target group (Hughes, 2005; Thomas Jr., 2004). Therefore, they often appear as authentic fans of a product.

Whereas viral marketing and buzz marketing stimulate the diffusion of the message via consumer-to-consumer interactions, guerrilla PR has evolved as an accompanying method for all guerrilla instruments to spread the message via the editorial section of the media (Hutter and Hoffmann, 2011a). Thus, it can be considered a subtype of public relation. Guerrilla PR markedly improves the guerrilla effect since media reports increase the number of addressees at hardly any financial efforts. Guerrilla PR is very persuasive, because consumers consider press reports more credible than advertisements. To boost the efficacy of guerrilla campaigns by guerrilla PR, marketers need to plan the campaigns in such a manner that they are appealing for the journals (e.g., eye-catching ambient installations or activities of sensation marketing).

Low cost effect
Rationale: Two characteristics of guerrilla campaigns evoke a low cost effect. First, the diffusion effect helps to reach a wide audience causing no or little costs, because consumers (viral marketing) or the media (guerrilla PR) pass on the advertising message (path 5 in Fig. 1). Second, guerrilla campaigns are frequently implemented in such a manner that they require little monetary efforts (path 6 in Fig. 1). Many marketers apply a free riding approach to cut costs and raise the number of recipients simultaneously to maximize the low cost effect. For instance, they attempt to benefit from placing advertisements at big events (e.g., sporting events) without paying for it (path 7 in Fig. 1). Note that even if a campaign requires intensive investment, the diffusion effect assures that a wide audience is reached with an advertising which will decrease the relatively costs (the monetary effort per person reached).

Instruments: Ambush marketing is the most prominent distinct guerrilla instrument that focuses on keeping expenditures on a low level. It explicitly builds on a free riding effect (Andreoni, 1988; Kim and Walker, 1984; Marwell and Ames, 1981). Meenaghan (1994) defined ambush marketing “the practice whereby another company, often a competitor, intrudes upon public attention surrounding the event, thereby deflecting attention toward themselves and away from the sponsor”. Ambush marketing and sponsoring have in common that marketers use an event to promote their brands or companies. In contrast to sponsoring, ambush marketing aims at benefitting without having legal permission (Payne, 1998; Townley et al., 1998) and without having the duties of an official sponsor (Farrelly et al., 2005; Seguin and O’Reilly, 2008; Shani and Sandler, 1998; Tripodi and Sutherland, 2000). Marketers use this parasitic behavior for benefitting from an image transfer from an event to the company at low costs and for weakening the main sponsor. Accordingly, ambush marketing is often considered a direct competition between the official sponsors and the ambusher (Burton and Chadwick, 2009).

PROPOSITIONS FOR FURTHER RESEARCH

Although guerrilla marketing is applied more and more often in marketing practice, there is a lack of accompanying research. From both, a theoretical and an empirical point of view, little is known about how different guerrilla measures affect consumer attitudes towards the advertising company and the product. To fill that void, further research needs to develop models that explain how different guerrilla instruments affect consumption decisions. Moreover, evaluative studies should test these models and assess the advertising efficacy of different guerrilla instruments. Reliable and valid measures of the efficacy of guerrilla campaigns are needed to achieve these objectives. Finally, scholars have to generate guidelines on how marketers should plan, implement, and evaluate guerrilla campaigns. As an impulse for closing these gaps, we propose an agenda for further research from a consumer behavior perspective and a managerial perspective.

Consumer behavior perspective: Scholars can measure the impact of guerrilla campaigns in several different ways (attention, attitude towards the advertisement, corporate reputation, sales figures etc.). Moreover, the evaluation of guerrilla campaigns should take into account that each guerrilla instrument (e.g., viral marketing, ambient marketing, ambush marketing) evokes specific effects. Accordingly, the analysis of guerrilla effects is highly complex because different instruments, different moderating and mediating factors, as well as different evaluation criteria have to be taken into account. We suggest a general research framework to categorize and systemize further research on consumers’ reaction on guerrilla campaigns (Fig. 2).

Idiosyncratic behavioral models for each guerrilla instrument: Consumer’s reactions to guerrilla campaigns might fundamentally differ from the reactions to classical advertising, because guerrilla advertisements are highly unconventional. They do not match to consumers expectations about advertising and therefore they might be assessed independently from consumers pre-existing attitudes towards advertising. Guerrilla marketing occurs in unconventional places and via unconventional media and it explicitly attempts to provoke a surprise and a diffusion effect.

Fig. 2:	Framework for research on guerrilla effects from a consumer perspective

Thus, models of the effect of classical advertisements are not fully adequate to evaluate guerrilla effects. Scholars need to adjust and extend these models or they have to develop new specific models on the affective, cognitive and conative effects of guerrilla campaigns.

Note that one comprehensive model cannot feasibly display all the effects that different guerrilla instruments evoke. Each instrument (e.g., ambient marketing, viral marketing) elicits various cognitive and affective processes. Therefore, we suggest developing specific models concerning the advertising effect (e.g., the basic guerrilla effect) for each instrument individually. So far, researchers have already considered some instruments separately, such as viral marketing (Brown et al., 2010; Henning-Thurau et al., 2004), buzz marketing (Notarantonio and Quingley Jr., 2009; Thomas, 2004) or ambush marketing (Burton and Chadwick, 2009; Quester, 1997). Further research should develop models for the remaining instruments. Subsequently, scholars should extract a more general guerrilla approach by examining in which way these models overlap.

Downstream variables of the chain of effects: To date, scholars mainly discuss how guerrilla campaigns help to attract consumers’ attention (Siefert et al., 2009) and to stimulate a WoM process (Derbaix and Vanhamme, 2003). Future studies should take into account other outcome variables, such as the impact on brand awareness, the image of the company and customer loyalty (Thorson et al., 1992). Further research should refer to existing models of advertising effectiveness to describe the chain of effects from attention to these downstream criteria. The attitude towards the ad-model (Lutz et al., 1983), for instance, helps assessing the effects that the attitude towards a specific guerrilla instrument elicits on the attitude towards the brand. Furthermore, researcher should adopt advertising models that explain how surprise is evoked by incongruence and inconsistency (Heckler and Childers, 1992; Houston et al., 1987; Lui and Brewer, 1983), absurdity (Arias-Bolzmann et al., 2000), humor (Eisend, 2009; Flaherty et al., 2004; Hadley and MacKay, 2006; Schwarz and Hoffmann, 2009) and shock (Dahl et al., 2003; Manceau and Tissier-Desbordes, 2006). Although it is desirable that these factors evoke a certain level of activation, they should be implemented carefully. If the disconfirmation of expectancies is too strong the addressee may not able to assimilate it and the activation potential is reduced (Berlyne, 1963). Hence, further research should clarify whether the surprise effect is steadily increasing with the level of inconsistency and or if there is an optimal point on a certain level.

Unintended effects: Some guerrilla activities are on the brink of legality. In particularly, ambush activities sometimes cross legal and ethical limits (O’Sullivan and Murphy, 1998; Townley et al., 1998). Other actions (like ambient marketing) enter areas which used to be free of advertisements. Some consumers might consider them as a commercial intrusion in one of the last private areas disturbing the calmness and aesthetics of their natural surroundings (Kimmel, 2005). Facing these disadvantageous side effects, future research should consider possible negative consequences of guerrilla campaigns.

Of course, provocative campaigns can raise attention which is the primary objective of guerrilla campaigns. Importunate advertising in natural environment, however, might also evoke disappointment, sadness, anger, and fury. Presumably, the interplay of increased attention and these negative affects has a strong negative impact on the downstream criteria of the chain of effects (e.g., image, purchase intention, loyalty). Thus, further research needs to investigate which conditions drive consumers to dislike and reject a certain guerrilla campaign. Since negative mood reduces the advertising effectiveness (Hirschman and Stern, 1999), scholars should investigate how negative emotions evoked by guerrilla actions and negative evaluations result in a negative company image or the denial of purchasing its products. Future research is asked to identify potential risks and to provide solutions on how to avoid these risks (Dardis, 2009; De Pelsmacker and Van den Bergh, 1996). Moreover, scholars have to discuss guerrilla activities (i.e., ambush marketing) from an ethical point of view. As many consumers attach value to the ethics of advertising (Drumwright and Murphy, 2009; Townley et al., 1998), ethical aspects should be taken into account when analyzing the attitude toward the ad and toward the brand. In case of a clearly infringement of a right, marketers should consider legal conditions, such as copy trademark and property right as well as fair trade law and law against restraints on competition. To date, the legislation of many countries does not regulate and punish ambush marketing. Presumably, the legal practice will change in future times.

Moderator variables: The way how guerrilla campaigns influence different criteria of the chain of effects presumably depends upon several moderator variables. The branch (e.g., high-tech vs. food), the type of the company (e.g., SME vs. global player) and the kind of product (high vs. low involvement or consumer good vs. services) might influence the efficacy of guerrilla campaigns. In particular, further research should investigate whether only young enterprises (e.g., innovative start-ups) and small and medium sized enterprises can feasibly apply guerrilla marketing or if traditional companies (e.g., in the financial sector) and multinational enterprises can also benefit from guerrilla campaigns. Presumably, the target group of the company is the most relevant moderator. Maybe the efficacy of guerrilla campaigns is contingent on socio-demographic variables of the consumer, such as age, gender, education (Schwarz and Hoffmann, 2009; Hoffmann et al., 2010, 2011). More likely, the efficacy depends on personal characteristics, such as the consumers’ need for cognition (Reinhard and Messner, 2009), openness for new experiences (Jones et al., 2009), innovativeness (Hoffmann and Soyez, 2010) and sensation seeking (Galloway, 2009).

Managerial perspective
Creativity process: Advertisers are well advised not to copy existing campaigns because imitations are neither novel nor unconventional and, thus, they cannot evoke a surprise effect. The campaigns of the pioneering company are far more surprising and effective than the campaigns of those who copy or adopt extant guerrilla approaches. The perception of guerrilla campaigns changes over time and in accordance to technical developments and customers’ experiences. In order to design surprising campaigns, advertisers need to launch the right activity at the right time. Only if advertisers know the habits and expectations of their target group, they can evoke surprise effect and diffusion effects. Generating new ideas requires an extensive effort of research and planning. The required time and the resulting costs have to be considered in the calculation of the guerrilla campaigns return on investment. Further research has to advice managers how to stimulate the creativity process in order to create a surprise effect.

Efficacy and success drivers: Considering stagnating or shrinking marketing budgets, the appropriation of each advertising spending has to be put on a rational basis (Broadbent, 1989). Accordingly, the criterion of advertising efficiency is becoming steadily more important. Guerrilla marketing claims to achieve a highly efficient ratio of costs and benefits due to the surprise effect, diffusion effect and the cost effect. Note that this rationale does not imply that guerrilla campaigns are necessarily cost saving. If the benefits of an expensive campaign are high enough, the ratio is still effective. High benefits result from attracting the attention of numerous people (diffusion effect) by surprising them (surprise effect). Accordingly, cost-intensive campaigns belong to the concept of guerrilla marketing as long as they evoke a strong surprise effect and diffusion effect. Further research should compare the efficacy of different guerrilla instruments (e.g., ambient, viral, ambush) with regard to the three effects and with regard to their overall efficacy. Scholars need to investigate the conditions (e.g., branch, product type, target group, corporate image, and marketing budget) for an appropriate use of the various guerrilla instruments. The success drivers of guerrilla campaigns (e.g., messages, products, target groups, locations, humor etc.) should be identified. Presumably, there are no monocausal explanations. In contrast, guerrilla campaigns are presumably most effective if they reasonably fit to the company, the product and the target group.

Assignability: Companies benefit from guerrilla activities only if consumers ascribe the action to the company or the product. If consumers associate the campaign with no enterprise or product, the company has to bear the costs without gaining any benefit. If consumers relate the campaign to a competitor, the proportion is even worse. For that reason, guerrilla advertisers must not solely focus on the creation of a surprise effect. They have to ensure that consumers assign the campaign to the company. If the company is not recognized as the origin, a competitor can adopt the idea and take advantage of the surprise effect and the attention of the customers. Thus, further research should investigate on how marketers can assume that consumers expose to a guerrilla activity and foster identification toward the company or brand. Marketers need to know how obvious these cues should be. Presumably, the cues need to be clear enough to identify the company but they must not be too importunate in order to prevent active brand avoidance.

Implementation and controllability: Due to the flexibility and the spontaneity needed for guerrilla marketing, it is doubtable whether marketers can feasibly plan and control the diffusion of a guerrilla campaign. Further research should analyze how and when guerrilla activities develop an own dynamic once implemented (Zuo and Veil, 2006). Additionally, scholars should analyze how guerrilla campaigns interact with other marketing activities and the public communication. In particular, negative media reports have to be considered. Presumably, companies are well-advised to implement managers who are responsible for guerrilla marketing and equipped with a defined budget. In this way, there is one single person or group, who can flexibly react to actual developments within the framework of the predefined marketing strategy.