I think there is a question over what actually constitutes sniping... Are you considered a sniper at 15 seconds? 30 seconds? 2 minutes?
Some sellers get angry if you place a bid within the last 5 minutes of an auction and consider that sniping.
I am not sure why some sellers dislike the practice, for if it wasn't for that last second bid, the price would have been lower anyway.
No one is preventing anyone from bidding, because the time on the auction determines the last bid.
Anyway, to further answer your question and to echo Bartelby, the seller doesn't have any specific evidence that you were planning a snipe unless you leave the checkbox checked that you send them a notification telling the seller you won the item using Auction Snipe.
-bjt