A bid snipe is a last minute bid in a timed auction which is designed to allow the sniper to win the auction with a decisive bid which no one else can beat because the auction closes almost immediately after the bid is placed. Bid sniping is most commonly seen in online auctions, and the practice is not without controversy. Some people swear by sniping, arguing that it's the best way to bid for items they like, while others find sniping very frustrating because they routinely lose auctions to snipers.
In a classic timed auction, people participating in the auction can see whenever a new bid is made, and decide whether or not to match it. There are a number of bidding strategies in use, ranging from strategies which create bidding wars early to drive off competitors to bid sniping, in which someone holds off until the last minute. Bid sniping can be advantageous because it reduces the risk of a bid war, and because it keeps a bidder's identity hidden so that other bidders cannot see who is interested in an item.
Bid sniping can be done manually or with an automated system. When people bid snipe manually, they simply wait until the auction is almost up, manually entering a bid in the last few seconds. This can be unreliable, as sometimes the bid doesn't get in before the auction window closes, or the bidder experiences problems with the bidding process such as a momentarily lagging server which causes the bid to hang, rather than going through.
With software, bidders enter the auction they are interested in, and determine the maximum amount they are willing to pay. The software is directed to place a bid at the last second, with the bid snipe being slightly higher than the most recent bid so that it will win. However, if multiple people try to bid snipe on an item, the software may not be able to keep up fast enough to ensure a win.
In addition to using software, people can also use a bidding service, hiring someone else to do their bid sniping for them. Services typically charge a fee on the basis of the final auction price. People can only use these services in auctions which allow proxy bidding.
Some auctions have specifically banned bid sniping, although the practice is largely permitted, even though some users do not like it. Users who aren't sure about whether sniping is allowed can read the terms of service for an auction website, or contact the customer service department of the company administering the auction to determine whether or not a bid snipe is permissible.