eBay could put a limit on the number of retractions and backings out a buyer can make. That would help with the serial bid retractors, while allowing for a few honest mistakes.
I can understand a mistake bid or two, but don't know how someone could make more than two a month. Stay off the sauce. I recall making one and that was about fifteen years ago. I typed in an extra zero in my bid. If you're making five or ten a week, I think it can be safely defined as abusing the system.
I do agree that backing out of winning bids is a bad idea for auctions. For centuries the entire auction process has been based on the saying and rule "Goes to the highest bidder." The seller is required to sell to the highest bidder and, if the bidder can't or won't honor his bids, he's not supposed to be participating. Some would compare not honoring your winning bids to not honoring your gambling debts.
There's an entire Laurel and Hardy short about a grandfather clock they have to carry home after accidentally placing the winning bid on it at an auction and being threatened over if they didn't pay what they owed. Alas, the clock is run over by a car before they can get it home and Oliver's wife isn't too happy about his expenditure on a pile of scrap wood.
But, as I said, an honest error in bidding once in a while is understandable and excusable.