Thats what I do, won a running mini bike last week for $82, set my high bid at $100. Its an old school 5hp briggs and stratton one. Can't wait until camping season to ride it around the campground.
So I have another toy I wanted as a kid, now off to find another.
The problem is that with the eBay limit set, the other bidders immediately know they've been outbid by someone's limit, and can re-bid again. Or a dishonest seller with his own shill account can keep pumping it up closer to your set limit.
Let's say there's two people interested in an auction. You and another bidder. The other bidder puts in a bid of $90 into eBay. You put a limit of $100 into eBay, the other bidder knows immediately to keep on bidding until either he gives up or he surpasses your limit outbidding you.
With the sniper program, your max. bid is witheld from eBay and everyone else until the last possible second. Using the sniper program, the other bidder would only see his max bid of $90 sitting there alone up almost until the auction ends. The sniping program with a few seconds to go will enter a bid of $91, and you win the item.