A growing number of digital platforms operate in a dual mode: running marketplaces for third‐party products, while selling their own products on those marketplaces. We build a model to explore the implications of this controversial practice. We analyze the tradeoffs that arise from a regulatory ban on the dual mode, showing how such a ban can harm consumer surplus and welfare even when the platform would otherwise engage in product imitation and self‐preferencing. In the empirically most relevant scenarios, policies that prevent platform imitation and self‐preferencing generate better outcomes than an outright ban on the dual mode.

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Platforms that intermediate trades—such as Amazon, Airbnb, and eBay—play a regulatory role in deciding how to govern the marketplaces  they create. We propose a framework to analyze a platform’s nonprice governance design and its incentive to act in a welfare-enhancing manner. We show that the platform’s governance design can be distorted toward inducing insufficient or excessive seller competition, depending on the nature of the fee instrument employed by the platform. These results are illustrated with micro-founded applications to a platform’s control over seller entry, information provision and recommendations, quality standards, and search-design choices. (JEL D21, D83, L15, L23, L81, M37)

The maintenance of cooperative behavior is fundamental for the prosperity of human societies. Empirical studies show that high cooperation is frequently associated with the presence of strong social ties, but they are silent on whether a causal mechanism exists, how it operates, and what features of the social environment are conducive to its emergence. Here we show experimentally that strong ties increase cooperation and welfare by enabling the emergence of a close-knit and strongly bound cooperative elite. Crucially, this cooperative elite is more prevalent in social environments characterized by a large payoff difference between weak and strong ties, and no gradation in the process of strengthening a tie. These features allow cooperative individuals to adopt an all or nothing strategy to tie strengthening based on the well-known mechanism of direct reciprocity: participants become very selective by forming strong ties only with other cooperative individuals and severing ties with everyone else. Once formed, these strong ties are persistent and enhance cooperation. A dichotomous society emerges with cooperators prospering in a close-knit, strongly bound elite, and defectors earning low payoffs in a weakly connected periphery. Methodologically, our set-up provides a framework to investigate the role of the strength of ties in an experimental setting.