The aim of this paper is to show that an intermediary can, paradoxically, encourage opportunism among players in regulated coopetition under certain conditions. Contrary to what the literature advocates, the intermediary will henceforth have an ambivalent role. We have adopted a mixed-method approach, specifically using the comparative qualitative analysis in its multi-value version. The theory of justice and equity was used to explain the intermediary's position when faced with the opportunistic behavior of coopetitors. The primary data came from a questionnaire administered to 48 coopetitors in the transport sector in the Owendo commune of Gabon. The results indicate that the intermediary has an impact on the opportunistic behavior of the coopetitors by paradoxically encouraging distrust or trust between actors; paradoxically and progressively, by punishing cheating coopetitors, starting with raising awareness, then reproaching them, and finally punishing them; encouraging an increase in actors' revenue; paradoxically balancing competition and cooperation or favoring competition to the detriment of cooperation; or maintaining the good or bad reputation of the actors. Therefore, the intermediary causes opportunism. Our results also show that players use opportunism to counteract the unfairness and inequity of the intermediary. Theoretical and managerial contributions are suggested.