On sellers' cooperation in hybrid marketplaces

Hybrid marketplaces, such as Amazon's and Zalando's stores or Apple's Google's app stores, which distribute their own products services in competition with those of third-party sellers, play a significant growing role the Internet economy. This paper shows that, other things equal, platforms would maximize profits if they lowered fees charged to sellers prices consumers response cooperation agreements between sellers: horizontal mergers collusive agreements. It also that can be pro-competitive when platform is vertically integrated gatekeeper, adopts agency business model, close competitor it hosts, observes (or correctly anticipates) sellers' agreement. The discussion here policy relevance, since online marketplaces may find easier collude respond bargaining power certain gatekeeper by merging activities.