Lecture on the first SFB/TR 15 meeting, Gummersbach, July, 18 - 20, 2004: We develop a general theoretical framework of trade on a platform on which buyers and sellers interact. The platform may be owned by a single large, or many small independent or vertically integrated intermediaries. We...

Increased competition tends to benefit all buyers with increasing product variety and decreasing prices. However, if local and external market channels compete for the same class of products, increased competition from the external market crowds out local variety. Under local monopoly, local...

We develop a model of search among substitutes for the best combination of commodity variant and price, in which the structure of search costs is manipulable by the suppliers of these variants, e.g., by joining an existing market or opening a new one. We analyze the subgame-perfect equilibria...

We examine the design of nonlinear prices by a multiproduct monopolist who serves customers with multidimensional but correlated types. We show that the monopoly can exploit the correlations between consumers' types to design pricing mechanisms that fully extract the surplus from each consumer....