Journal article: Of primary importance in auction design is the set of strategies available to the seller at the auction stage. We first formalize hold-up regarding entry costs that preys on second-price auctions when the seller may engage in a costly shill-bidding activity. We derive the optimal reserve and show how shill bidding can make posted prices outperforming auctions. Second, we advocate for a new regulation where shills would be banned but with the possibility of canceling sales ex post, which offers some valuable flexibility: the English auction with jump bids implements, then, the first best in general environments.