Howard Wallace said:
You are agreeing to a contract -- You will enter into a legally binding contract to purchase the item from the seller if you're the winning bidder.
There is only a contract with the winning bidder. And there are still ways to back out of that (legally as well as per ebay rules). It's treated as a verbal agreement - in lawyer talk.
Let's say you have this porcelain dish you put for sale on ebay. Two days into the auction, your three-year-old tips it off the table and it smashes into a hundred pieces on the floor. You can no longer sell it. And no bidder in their right mind would want it anymore. So, eBay came up with a way that allows sellers to back out of the auction if the status of the item changed
relative to the description of it. One thing led to another and there are now several reasons why you can now dissolve an auction...including the very vague and often used: "Item is no longer available" (which I have used personally).
In order to cancel the auction for my now shattered dish, I would first cancel each bid individually (eBay's way of "punishing me" for backing out of the auction - make it painful/hard...I might give up

) and then once the auction has no bids, I could cancel it.
As long as there are more than 12 hours left.
I once had an item where I put in the description that it was for sale locally as well (also legal on ebay). It sold and I cancelled all the bids. Somebody kept trying to bid over and over again. I kept trying to cancel it, but in the end they prevailed in getting a bid in right at the 12 hour mark. I am not making this stuff up. It was 100% clear in the bid history that the item was "no longer available". It was also clear that every time this guy put in a bid, I was cancelling it. Thick-skulled, perhaps? Anyway, he "won" my item for like $9 (it was worth $500). Emails me with all sorts of demands, etc. So, I took the legal route and proved to eBay that I had tried to cancel his bid, but he was relentless, etc., etc. eBay sided with me on the issue. This guy was upset, but eventually got over it. The other bids I had cancelled were in the hundreds...what was he thinking? that he could just show up, sneak in, and steal it away from me?
Besides, it was actually already in the mail to the other guy.
Anyway, I've been with eBay since '97...and have seen lots of stuff come and go. Fascinating place. Lots of crooked people on there, though. Definitely need to read the fine print - all of it.