The user agreement clearly sets forth that the seller is obligated to complete the transaction if he receives at least one bid above the minimum or reserve.

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 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.

If I am obligated to buy when I bid, then the Seller is obligated to sell.