As far as I know, Listia doesn't allow for canceling of a bid by the bidder, and I can't do so as a seller either. The seller can prevent a bidder from bidding by banning them, but I don't know whether that would cancel current bids and it then also prevents all communications between that bidder and the seller... Guess you can just hope that someone outbids, alternatively if you win, you could file a dispute a few days later and get the credits back.