Sniper bidding is having software enter your highest bid on an item shortly before that auction ends.  I use AuctionSniper, but there are many other programs available.  eBay uses a proxy bidding system.  Many newcomers don't really understand this option, so they don't understand how sniping is just a logical extension.  When you enter a bid, that is not necessarily the price you will pay - eBay checks your bid against all others and sets your bid at just enough to beat the closest bid. Eg, if you bid $20, and the highest bid is $12.25, you'll get the auction for $12.50.  eBay displays the current high bid. A sniping program waits to submit your bid until just before the auction ends.  By using this method, you avoid bidding wars, and you dont have to be online when the auction ends. 

Sniping seems to bring out strong reactions, especially those who  think sniping is either unfair or unethical.

I dont see any real basis for this to be an ethical problem.  Firstly,, eBay at least considers them ethical, since they do not ban or otherwise prohibit them [while they do ban shill bidding, bidding circles, etc].   - if it's the fact that sniping companies get paid, what would you think of sniping done by individuals who write their own software [not that difficult to do]?  Sniping isnt much different than any silent auction, where no bids at all are revealed until the end.  and as far as the cost, my monthly sniper fees are MUCH less than i would otherwise have overbid on individual auctions.

For fairness, again, i dont see any issues - sniping programs are available to anyone who wants to use them;  you CAN'T be outbid if you enter the most you would pay for an item; plus, you dont get caught in the psychological trap of bidding more at the last minute because "it's just another $1".  for this latter reason, a good argument is made that sniping actually lowers the final auction price, since there are fewer last minute bidding wars.

as a trader, sniping has become essential for me - especially areas where i may place 100 bids a week, hoping to win about a dozen.  sniping lets me make a unstressed, rational decision, and then let the auction proceed.  i can bid on auctions that end at any time, since i dont have to be there to follow them.  also, if you're trying to buy one particular item, sniping can be set up so that once you win that item, no further bids are put in.  this is a great aid when you're bidding on a popular item [digital camers, popular DVD sets, etc] - no need to bid one at a time on auctions to prevent winning several of the same item.