You have bids so it would be a very poor sellin practice to withdraw now.
Your bidders are bidding in good faith with the reasonable expectation that you will fulfil your obligations.
People asking for BIN are usually hoping to get the item for less than they think it might reach at auction.
Invite them to bid with the otheres, if they really want the item they will bid. If they don't, you will know they are just timewasters trying to get something on the cheap.