Bidding and Buying.
As a buyer, you have a legal obligation to complete a transaction with a seller:
if you purchase an item through one of our fixed price formats; or
b. if you are the highest bidder at the end of an auction-style listing (meeting the applicable minimum bid or reserve requirements and including any bid that becomes the highest after a valid bid retraction) and your bid is accepted by the seller, unless the item is listed in a category under our Non-Binding Bid Policy or the transaction is prohibited by law or by this User Agreement.
By bidding on an item you agree to be bound by the conditions of sale included in the item's description provided that those conditions of sale are not in breach of this User Agreement or otherwise unlawful. Bids are only retractable in exceptional circumstances, such as when the seller materially changes the item's description after a bid is placed, a clear typographical error is made, or you cannot authenticate the seller's identity. Please refer to our Bid Retraction Policy for further clarification. As buyer, you must ensure that you are legally able to bid for and buy any item that you bid for.
taken from ebays user agreement, I was talking from a contract point of view, ebay does claim to be only a trading platform, but the individual auctions that go on there would, I think, be interpreted in court as such. cds:)