The only time I've ever won a bid on Ebay was when I bid on an item that was so unusual that there wasn't a high demand for it. That plus the fact that it was used and I could have bought the same part new for a few bucks more, didn't really save alot. I've seen many items sell for more than they're worth, especially when there's times you could get the same thing or better new with a warranty, like if buying used parts, camera or PCs like a used, outdated laptop (w/o a warranty) for example.
Many times I'd have the item until the very last minute, then someone outbids me (marginally) and it's too late to get another bid in. When that happens, I suspect that something's not quite right there.