We consider situations where a sale affects the ensuing interaction between potential buyers. These situations are modeled by assuming that an agent who does not acquire the object for sale incurs an identity-dependent externality. We construct a revenue-maximizing auction for the seller. We observe that: 1) outside options and participation constraints are endogenous. 2) The seller extracts surplus also from agents who do not obtain the auctioned object. 3) The seller is better-off by not selling at all (while obtaining some payments) if externalities are much larger than valuations.

We study the problem of a seller who wants to maximize her revenue in situations where the outcome of the sale affects the nature of the future interaction between agents. We model those situations by assuming that an agent that does not acquire the object for sale incurs an externality that may depend both on the identity of the sufferer and on the identity of the final purchaser. We describe an optimal auction that has a unique Nash equilibrium in strictly dominant strategies. We show that: 1) Outside options are endogenously determined in equilibrium. Participation constraints and the ''threats'' in case of non-participation play an important role. 2) An optimizing seller can extract surplus also from buyers that do not obtain the auctioned object. 3) The seller is better off by not selling at all (while obtaining some payments) if externalities are large when compared to the pure profits that buyers achieve if they acquire the object. 4) The revenue-maximizing equilibrium is coalition-proof if buyers cannot organize side payments among themselves. (orig.)