How is the supporting evidence unknowable? I've seen it repeatedly myself. When I first began buying on e-bay, I would naively put in my max bid days before the auction ended. I'd then get to watch as either incremental bidders eeked the price up slowly or as snipers bumped it at the last moment. Sometimes I won, more often I lost. Losing to the snipers is a no win situation - they were willing to pay more than I was, end of story. Had I sniped the same bid, I still would have lost. With the incremental bidders, I would up paying more than I otherwise would have, especially if it was only one other bidder.
Scenario 1 - you bid your max early, and there is a single incremental bidder. Item starts at $25. You're willing to pay $90. You bid $90. Chippy the incremental bidder comes along and decides he wants the item. It shows 1 bid, and a $25 price. He bids $27; your bid increments to $28. He chips up to $30; ebay bumps yours to $31. He goes $35, yours jumps to $36. He goes $40, $45, $50, $60 and finally quits at $75. Your bid now stands at $76. No one else bids. You win the item, for $76.
Scenario 2 - I see the item and decide to snipe. Chippy comes along, decides he'd like it and puts in his $30 bid. He's the high bidder at $25, and has no reason to go any higher, so he doesn't. I wait till five seconds are left, and bid $90. I'm now the high bidder at $31, and Chippy, even if he's watching, doesn't have time to react and bump his bid. I win the item for $31.
I'd rather pay $31 than $76. Wouldn't you?
Scenario 3 - once again, max bid early, same $25 start price, $90 max. Chippy once again bumps it up to $75. You're still winning. A sniper comes along, sees a bunch of bids and that it's way up at $76 and decides to bid $100. You lose at $91.
Scenario 4 - Same starting situation, but you decide to try sniping. Chippy bids $30; the item shows 1 bid at $25. The same sniper comes along sees little activity - only one bid. Decides to try for a bargain, and rather than bidding the $100 he would have bid when it was at $75, decides instead to only bid $60, as it looks to be going cheap. You snipe with your $90 bid, and though you bump into him, you still win at $61. A bit pricier, but better than losing out.
I personally, as a buyer, can see no downside (other than the inconvenience; I've not been inclined to try a sniping program) to sniping - only up sides. I may not win a LOT more auctions, but in the long run am most likely to pay less overall than those who place max bids and let the chips fall where they may.
I actually suspect that a lot of incremental bidders don't fully understand how e-bay's proxy system works which is why they chip away like they do, placing small incremental bids up to their max, and as such will stop incrementing as soon as they see they have the winning bid. If no one has bid on something, then they'll stop at one very low one.
FWIW.
-Pat