Auctioneers sometimes prefer entry fees to extra bidders

We investigate a market thickness–market power tradeoff in an auction setting with endogenous entry. We find that charging admission fees can sometimes dominate the benefit of recruiting additional bidders, even though the fees themselves implicitly reduce competition at the auction stage. We also highlight that admission fees and reserve prices are different instruments in a setting with uncertainty over entry costs, and that optimal mechanisms in such settings may be more complex than simply setting a reserve price. Our results provide a counterpoint to the broad intuition of Bulow and Klemperer (1996) that market thickness often takes precedence over market power in auction design.