Warrior,
There's always a chance (very, very, very unlikely) a last second snipe won't get placed, even if you use two sniping services. But, poop happens. The only guarantee that a bid will be placed is to place it through ebay in advance of the closing of the auction. BUT, you’ll lose the advantage of sniping, that of an increased likelihood of paying less. Guarantee – pay more; snipe – pay less.