I used to buy a lot on eBay and an awful lot I was offered the item I just lost for the underbidder price, and I came to think of them as "You were a giant sucker emails" and I almost always said "No thanks". Of course, sometimes that person who outbid me was a shill, and then I would have been stupid to pay the underbidder price, because there was no REAL high bidder.
We tried offering items at one bid over where the third bidder had bid for a while, but it resulted in few sales, so we quit it, and now we just re-auction the item, and strangely, a fair amount of time it goes for even MORE the next time (although sometimes it goes for much less).
1% of bad bidders doesn't sound like much, but when you auction 110,000 items a year, 1% is 1,100 items, and yes, we re-auction that many. And 1% of four million dollars is $40,000, so they do add up to a lot of money.
But it VERY rare that the same person gets us twice.