**5. Discussion**

Green marketing solutions enhance various indicators of customer behavior; however, to date, there has been a lack of a detailed specification of how strategic, tactical, and operational green marketing practices affect customer behavior at different stages of the customer decision process. To unlock this puzzle, we aimed to provide a comprehensive and systematic overview of green marketing and its impact on customers' purchasing behavior to develop a research agenda that helps to identify promising areas for future research. We reviewed a large body of literature with the chosen systematic literature review methodology. We explored the past 28 years of research concerning the impact of green marketing on customer behavior. Even though we have reviewed a large number of existing literature on the effect of green marketing on customer behavior, there may still be papers that were not examined in this study. Since the last time we conducted a search was May 2022, it is likely that some 2022 papers on this topic were not included.

After the comprehensive review of articles included in the analysis, we categorized green marketing factors into three categories based on the levels of green marketing. The most common viewpoint to green marketing initiatives is bounded by the tactical level of green marketing, particularly promotion. However, green marketing is not only about the promotion of green products; it is a strategy, as well—a strategy that implies a radical change in the vision to lead organizations and not only to generate profits through desirable consumption behavior [92].

In the literature, there are definitions of purchasing behavior that explain the concept as the customer's search, purchase, usage, appraisal, and disposal of products, services, or ideas in order to satisfy their needs [93] (p. 1682). With regard to measuring customers' green purchasing behavior, we have identified the metrics that fall into two categories based on the stages of the traditional customer decision process, i.e., purchase and postpurchase. Green marketing at the strategic level increases purchase interest, product preference, purchase intention, purchase behavior, consumption level, loyalty towards green products, and green-oriented store. Regarding the green marketing solutions at the tactical level, we have noticed that green product and green promotion impact the widest variety of customer-purchasing measures, while the impact of green processes manifests in purchasing behavior. In the studies reviewed, any combination of green marketing solutions at different levels did not seem as powerful as initiatives implemented on one specific level. Therefore, we assume that the synergy of green marketing solutions representing more than one level may not strongly impact customers' purchasing behavior. However, a short list of measures may not mean a slighter impact; the impact may be strong but not diverse in terms of measures. Additional empirical evidence is required to determine how different combinations of green marketing solutions representing strategic, tactical, and operational levels affect customers' behavior at the purchase and post-purchase stages. Therefore, the authors of this paper commit to carrying out an empirical study in European countries to test the possible relationships between green marketing solutions and customers' purchasing behavior.

At the purchase stage, green marketing solutions influence intentions and actual behavior. However, we have to note that "the intention to purchase does not always translate into actual purchase behavior when consumers are confronted with a purchase situation" [91] (p. 423). This means that there may exist a gap between planned and actual customer behavior. In such a way, the possible impact of green marketing may end at the intentions without proceeding to the actual and post-purchase behavior. Despite this limitation, most reviewed studies confirm that green marketing is a reliable and essential tool that significantly impacts customers' purchasing behavior in the challenging business environment.

The other limitation of this systematic literature review is related to the choice to concentrate exclusively on behavioral indicators. According to the theory of planned behavior, an important antecedent of behavioral intention is attitude. In the researched sample, there were studies [62,89,94–96] that involved attitudinal indicators (attitude towards the green purchase, attitude towards the advertisement, brand attitude, etc.) next to the behavioral ones. However, this systematic literature review did not cover them as they fall out of the scope of behavioral indicators. However, the authors of this paper endorse the impact of attitudinal measures in aiming for desirable customer behavior.

The systematic literature review is limited in the choice of databases (WoS, Scopus, and EBSCO). Including other databases, for example, ProQuest, Springer, ScienceDirect and others, could contribute to the search for studies on green marketing and its impact on customers' purchasing behavior. However, the chosen three databases assured the research area's reliability. With this limitation in mind, we recommend that future studies in the analyzed field include more databases (for example, ProQuest, Springer, and ScienceDirect) and search engines (for example, Google Scholar and Microsoft Academic).

One more limitation of the systematic literature review on green marketing and its impact on customers' purchasing behavior is that this review does not present the quantitative results of a meta-analysis. However, the collected amount of data regarding the effect of green marketing solutions on customers' purchasing behavior is vast, and the authors of this paper consider the possibility of using this data in the future for a thorough meta-analytic structural equation modeling study of green marketing factors affecting customers' purchasing behavior.

The results of our literature review suggest the following research recommendations:

1. Much of the existing research supports green marketing only at the strategic or tactical level. We assume that more studies should adopt green marketing at more than one particular level. A demand exists for an integrated view of green marketing to maximize the impact on customer purchasing behavior.

2. In light of an increasing number of works on green marketing and its impact on customer behavior, the topic seems to be under-researched in terms of the following sectors: industrials, health care, financials, utilities, and real estate.
