Targeted Advertising Platforms: Data Sharing and Customer Poaching

E-commerce platforms are rolling out ambitious targeted advertising initiatives that rely on merchants sharing customer data with each other via the platform. Yet current platform designs fail to address participating merchants' concerns about customer poaching. This paper proposes a model of designing targeted advertising platforms that incentivizes merchants to voluntarily share customer data despite poaching concerns. I characterize the optimal mechanism that maximizes a weighted sum of platform's revenues, customer engagement and merchants' surplus. In sufficiently large platforms, the optimal mechanism can be implemented through the design of three markets: $i)$ selling market, where merchants can sell all their data at a posted price $p$, $ii)$ exchange market, where merchants share all their data in exchange for high click-through rate (CTR) ads, and $iii)$ buying market, where high-value merchants buy high CTR ads at the full price. The model is broad in scope with applications in other market design settings like the greenhouse gas credit markets and reallocating public resources, and points toward new directions in combinatorial market exchange designs.