PurposeThis study aims to identify which elements of the vending marketing mix are the main sources of competitive advantage for the industry, how they impact vending profitability, and what are their related synergistic effects.Design/methodology/approachA full factorial experiment was developed to determine the effect of eight marketing mix scenarios on the profitability of a new vending channel in a French university library and assess the synergistic effects among three elements of a marketing mix (i.e. product quality, payment system, internal location) identified in a focus group as new sources of industry competitive advantage.FindingsAlthough the main effects of product quality and payment system were weak-to-modest and insignificant, their interaction effect significantly impacted the daily net profit of the vending channel and generated the highest net synergy. The results partially challenge the marketing synergy axiom as internal location separately had a stronger impact on profitability than product quality and higher-order interaction effects do not necessarily translate into higher synergistic effects.Research limitations/implicationsThis research was conducted in a real-life setting and has its limitations, which future researchers can overcome by extending the temporal, geographic and product scope of the study.Originality/valueThe distinction that we introduced between gross and net synergy allowed us to partially challenge the prevailing marketing mix assumption that synergy is always positive (i.e. that a vending retailer can achieve synergy by selecting a combination of marketing mix elements instead of relying on them separately). Moreover, by demonstrating that marketing synergy is not a uni- but a bi-dimensional concept, we provide vending retailers with a better methodological understanding of why they may have already fallen into the synergy trap and how to avoid it in the future.