For the most part, I agree with David

Ending an auction early and cancelling bids to sell outside eBay is unethical. They were the vehicle for bringing the buyer and seller together, then get cut out of their share.

Ending an auction early because you decided not to sell the item after all isn't unethical. I changed my mind on a $1 Dunes that I still have.

Ending an aution with no bids is a gray area if you are selling off eBay - again the party that brought the buyer and seller together and got shut out on their cut so I'd say it's unethical - others would disagree.

I'd like to see the case law on auctions because as far as I know (and that ain't far) a contract is formed by offer and acceptance. A offers a chip for sale and B accepts by bidding $5, how is that not a contract?

My 2 cents!