I'm curious about them, too!
I don't know, but I don't see the point in them as a buyer. But people really seem to bid on them. I've seen them for gift cards (mystery amount between $5 and $500). I've seen them for Bath and Body Works products (products will be added as the bidding goes up and you will be surprised what's in the box). Some of them state that you're bidding on an envelope for the gift cards and the seller has no idea what the amounts are in the envelopes. You bid, you get an envelope mailed to you and that's what you get. Personally, as a buyer, I don't see what the draw is, but I obviously am uninformed because folks are always bidding on these types of auction, sometimes for lots of money.
On this board, I once asked why do folks bid the same amount or more for the value of a gift card, plus shipping, on eBay. I can't understand that one either.