This article is from the eBay FAQ, by William B. Shaw toppsoft@yahoo.com with numerous contributions by others.
Other than the joy of sniping, bidders generally snipe for three practical
reasons.
a. Since other bidders may not have bid their max, snipers can get bargains
by waiting until the last minute. Many bidders only bid enough to become the
high bidder without considering their max. Other bidders think they have bid
their max, but reconsider and are willing to go higher when the receive they
outbid notice from eBay.
b. Items with bids tend to attract more bidders. If the auction has little
activity, snipers perceive the auction will be overlooked by potential
bidders.
c. Some bidders are stalked by other bidders with similar buying interests.
After all, why should you search for auctions if someone else is doing the
work? By sniping the auction, the sniper prevents the stalker from placing a
competing bid.
 
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