To the best of my knowledge, eBay's proxy bidding system always wins out. So even if you place a snipe with just a second remaining, eBay will still have plenty of time to proxy bid for another user. Because of this, we suggest that you keep your lead times between 5 and 7 seconds.
The good thing about this is that many users don't rely on eBay to proxy bid for them because it drives up prices too quickly.
Adam R.
Auction Sniper Support