AS bids by logging in as you so how can any seller know unless you tell them?
Some sellers see sniping as a system that costs them money by eliminating bidding wars.
Some buyers see sniping as unfair or ungentlemanly.
Some buyers confuse eBay with a real auction where you start bidding at the start and keep bidding until someone wins. Fools!
Luckily more and more don't care any more...
R2