"Reactive" is a smoother word, but when I consider the definition of "sniper", I have a hard time visualizing a general ordering one of his soldiers to "react" to an enemy sniper.
Nibbling-sniper? Those bidders that start bidding in the last few minutes. They'll place several bids, but they are usually in small increments. They can place those snipes/nibbles/bids very quickly, because after the bid is place, ebay tells you, "Sorry sucker, but here's another bid field so nibble your brains out". Hasn't anyone ever encountered this?
P.S. Good morning Mrs. M and Steve.