Competing Combinatorial Auctions

We investigate if and how revenue-maximizing auctioneers restrict combinatorial bidding in the presence of auctioneer competition. Two sellers offer the same set of two heterogeneous items to six bidders in a VCG mechanism. Each bidder desires either the first item, the second item, or the package of both items. First, each seller decides on which packages to allow bids. Then, each bidder selects which of the two sellers' auctions to participate in. We find that, in contrast to a monopolistic seller, duopolistic sellers do not both offer an unrestricted VCG mechanism, i.e., a combinatorial auction. Rather they segment the market via their respective choice of allowable package bids: One seller attracts bidders who desire a single item; the other seller attracts bidders who desire both items.