On the pricing rule in electronic auctions

Researchers and experts have typically viewed electronic auctions (such as those implemented by eBay, Amazon, and Yahoo!) as either oral, ascending-price (English) auctions or second-price, sealed-bid (Vickrey) auctions. I show that important theoretical differences exist between English and Vickrey pricing rules and those used in electronic auctions, due to the presence of bid increments. I also show, using data on eBay laptop sales, that these differences have practical significance. I explore the implications of bid increments for strategic bid selection in a static model within the symmetric independent private-value paradigm. I derive the unique symmetric equilibrium bid function, showing that the presence of bid increments can significantly alter bidder behavior. Using numerical methods, I also illustrate that these result in a highly non-linear bid function, in contrast to that predicted under either the English or the Vickrey formats.