A second-bid auction is one where all bidders submit their maximum willingness to pay, and then the bidder willing to pay the most pays what the second-highest bidder was willing to pay. An English auction is where bidders submit bids which they will have to pay, with the idea that once the second-highest bidder will stop raising the bid once they pass their threshold.
There's a lot of theoretical work showing that second-bid auctions are all-around more efficient. English auctions can encourage the highest bidder to overbid, and the winner's curse refers to the phenomenon that the winner of an auction is generally the person who overestimated its value by the most. Second bid auctions mitigate that by making them pay only the second highest estimate.
If JohnWittle is the only bidder in the auction, then in a second-bid auction he would receive gwern's soul for free, but because this is an English auction, he has to pay his full bid, and so loses out for dramatically overestimating its market value- like gwern planned all along!
If JohnWittle is the only bidder in the auction, then in a second-bid auction he would receive gwern's soul for free,
Well, yes, technically that's true... but what prevents/discourages gwern (or his accomplice) from submitting an $N-1 bid (where N is the current sole bid amount)?
If it's worth saying, but not worth its own post (even in Discussion), then it goes here.