Here is a quote from Ebay's rules:

5.2 Binding Bids. Except for items listed in a category under the Non-binding Bid Policy, if you receive at least one bid at or above your stated minimum price (or in the case of reserve auctions, at or above the reserve price), you are obligated as the seller to complete the transaction with the highest bidder upon the auction's completion, unless there is an exceptional circumstance, such as: (a) the buyer fails to meet the terms of your listing (such as payment method), or (b) you cannot authenticate the buyer's identity.

This is a binding contract ya know!
Adam