I think it's been pointed out a few times that the optimal way to win an auction on eBay is not only to set your price in advance, but to only bid in the last second or two. By "sniping," you cut out everybody else's competitive desperation.
I know a few times, I've bid on something, then bid on it again immediately when it was out of my price range. That's some serious stupid. "Gee, someone else wants it. It's now worth more to me!"