Auction sniping is submitting your auction bid in the last seconds of an auction. When you snipe, you avoid bidding wars and don't leave enough time to other bidders to change their mind and increase their bid.
Here are some hard statistics about how much Gixen users save on average, divided by eBay marketplace (US, EU, UK, Australia, Canada). This is for how much lower users win items on eBay compared to their maximum bid.
|Currency||Average winning price||Average maximum bid||Savings|
While we do not have eBay's data to compare this to (eBay does not publish this), it's a reasonable assumption that the difference between winning price and maximum bid is significantly smaller than the numbers above.
Gixen is very inexpensive - base service is free, and premium ("Gixen Mirror") service is only around $6 a year, for unlimited sniping. Gixen has been around since 2006.