From eBay's terms of agreement....that you agree to, by using the website...
eBay is a Venue.
3.1 eBay is not an Auctioneer. Although we are commonly referred to as an online auction web site, it is important to realize that we are not a traditional "auctioneer." Instead, the Site acts as a venue to allow anyone to offer, sell, and buy just about anything, at anytime, from anywhere, in a variety of pricing formats, including a fixed price format and an auction-style format commonly referred to as "online auctions" or "auctions." We are not involved in the actual transaction between buyers and sellers. As a result, we have no control over the quality, safety or legality of the items advertised, the truth or accuracy of the listings, the ability of sellers to sell items or the ability of buyers to pay for items. We cannot ensure that a buyer or seller will actually complete a transaction. Consequently, we do not transfer legal ownership of items from the seller to the buyer, and nothing in this agreement shall modify the governing provisions of Ca. Com. Code § 2401(2) and Uniform Com. Code § 2-401(2), under which legal ownership of an item is transferred upon physical delivery of the item to the buyer by the seller.
Read the whole agreement here...