I've been using eSnipe since it first started. In over 8000 bids they've missed 3 bids, 2 because their server was down for a few minutes and once because eBay screwed up. I have no idea why any of the complaints have happened, but I've never seen anything like them happen. No other site I tried have ever come close to eSnipe. Unless there is one I don't know about, this is the best out there.
I have no connection with eSnipe except as a user.