Shill bidding and information in eBay auctions: A Laboratory study

Abstract

In online auction platforms, like eBay, sellers have frequently been observed to bid on their item to artificially increase its price, and this is known as shill bidding. We represent the eBay auction in a sequential auctions environment using lab experiments and study the behavioral consequences of sellers being able to participate as shill bidders and of being informed about buyers’ past bidding histories. We find that the possibility of shill bidding in ongoing and future auctions benefits sellers and mostly affects high private-value buyers. At the same time, buyers seem to overreact to the threat of shill bidding in the future auctions by biding too high in the current auction. However, providing sellers with buyers’ bidding histories between auctions has little impact on auction outcomes and players’ bidding behavior. Moreover, there are significant differences between buyers’ and sellers’ dynamic bidding behavior during auctions, which can be used to identify shill bidding sellers from buyers.