Sniping is, generally speaking, placing bid in on-line auction in the closing seconds. Of course, if you have superb Internet connection, exact watch, nerves of steel and the free time excess, you can do it manually. Snip.pl is an on-line auction sniper, it automates the last second bidding process and frees you from the trouble of remembering the ending time of each auction you want to bid on. Snip It! button lets you instantly schedule snipes at Snip.pl while browsing eBay, without the hassle of entering item ID by hand. Snip.pl is working for over 15 years.
Is it legal?
Yes. All bids placed within listing time frame are valid. Here's quote from eBay help: "Placing a high bid in the closing seconds of an auction-style listing is called “sniping” within the eBay community. Sniping is part of the eBay experience, and all bids placed before a listing ends are valid, even if they're placed one second before the listing ends." (http://pages.ebay.com/help/buy/outbid.html)
How does it work?
Bids placed with Snip.pl are exactly the same as if they were placed by hand. Exactly the same. Snip.pl is not a "hack" to eBay site. It obeys all and all eBay's rules. What is different, is that the whole process is fully automated, so you don't have to do anything.