I guess I should weigh in on this since I am recently guilty of this too. Normally I would not cancel an auction because I think the best price would be attained by letting it run, but I sold a frame off ebay to a list member last week. I had just listed it that day and it had not met reserve yet altough it had a couple bids (including his). He bought another frame I had on ebay that same day by being the high bidder, and made an offer that was higher than I expected to get for the one I had just listed, so I took it and ended the auction. I would not shut down an auction that had met reserve or I felt would get a higher price than what was offered but in this case it seemed like the best course. I don't think I would have done it for someone not on the list or that I didn't already have some history with, as it is risky. But as long as you are playing by ebay's rules then why would you not want to maximize your opportunity? Some people state in their auctions "subject to prior sale" and I don't think ebay frowns on it. When you cancel an auction first you have to cancel all bids, and have to state one of certain listed reasons for this. One of the listed reasons is "this item is no longer available for sale". I can't think of any reason why they would put that in there unless it was ok to sell off ebay (OK I suppose an earthquake could have swallowed it up) As long as you own the item you should be able to sell it to whomever and however you want. After all, a seller is selling stuff on auction not for entertainment value, but to get the best price he can. Ebay has rules to make their auctions fair and available to all, and also safe. I don't think they would allow you to cancel an auction if there were strong sentiment against it or it was somehow illegal. There is certainly no incentive for ebay to allow this, since they lose the potential final fee.
A similar argument could be made about the ethics of sniping. I use sniping software because ebay's system almost demands it. Heck, they created sniping. They set up their auctions so you must choose an ending time ahead of time, so it is the highest bid but also usually the last bid that gets the item. If they allowed you to close the auction when you thought it had reached its best bid, then sniping would not happen. Yahoo auctions allow this. You can extend an auction if you feel like it might go higher. It is very frustrating to a buyer. So is sniping ethical? You be the judge but I believe most experienced ebay buyers do it. I have certainly been "outsniped" a number of times. It is just part of the game so I don't get too upset about it.
Bob Freeman Seattle (where some areas had a white Christmas)