Abstract Suppose an intermediary provides a benefit to buyers when they purchase from sellers using the intermediary’s technology. We develop a model to show that the intermediary would want to restrict sellers from charging buyers more for transactions it intermediates. With this restriction an intermediary can profitably raise demand for its services by eliminating any extra price buyers face for purchasing through the intermediary. We show that this leads to inflated retail prices, excessive adoption of the intermediaries’ services, over-investment in benefits to buyers, and a reduction in consumer surplus and sometimes welfare. Competition among intermediaries intensifies these problems by increasing the magnitude of their effects and broadening the circumstances in which they arise. We discuss applications to payment card systems, travel reservation systems, rebate services, and various other intermediaries.

Optimal Auction Design and Equilibrium Selection in Sponsored Search Auctions by Benjamin Edelman and Michael Schwarz. Published in volume 100, issue 2, pages 597-602 of American Economic Review, May 2010

We investigate the "generalized second price" auction (GSP), a new mechanism which is used by search engines to sell online advertising that most Internet users encounter daily.GSP is tailored to its unique environment, and neither the mechanism nor the environment have previously been studied in the mechanism design literature.Although GSP looks similar to the Vickrey-Clarke-Groves (VCG) mechanism, its properties are very different.In particular, unlike the VCG mechanism, GSP generally does not have an equilibrium in dominant strategies, and truth-telling is not an equilibrium of GSP.To analyze the properties of GSP in a dynamic environment, we describe the generalized English auction that corresponds to the GSP and show that it has a unique equilibrium.This is an ex post equilibrium that results in the same payoffs to all players as the dominant strategy equilibrium of VCG.

We investigate the “generalized second-price” (GSP) auction, a new mechanism used by search engines to sell online advertising. Although GSP looks similar to the Vickrey-Clarke-Groves (VCG) mechanism, its properties are very different. Unlike the VCG mechanism, GSP generally does not have an equilibrium in dominant strategies, and truth-telling is not an equilibrium of GSP. To analyze the properties of GSP, we describe the generalized English auction that corresponds to GSP and show that it has a unique equilibrium. This is an ex post equilibrium, with the same payoffs to all players as the dominant strategy equilibrium of VCG. (JEL D44, L81, M37)