  We provide the first direct test of how the credibility of an auction format
affects bidding behavior and final outcomes. To do so, we conduct a series of
laboratory experiments where the role of the seller is played by a human
subject who receives the revenue from the auction and who (depending on the
treatment) has agency to determine the outcome of the auction. Contrary to
theoretical predictions, we find that the non-credible second-price auction
fails to converge to the first-price auction. We provide a behavioral
explanation for our results based on sellers' aversion to rule-breaking, which
is confirmed by an additional experiment.
