Stop harping about the US law. This is not a court case.
You're not just the auctioneer. You're the seller too, no commission involved here, so you can bid a millions bucks and essentially cancel the auction without explicitly doing so. It's a shitty thing to do, particularly since you hadn't disclosed that option in advance. Why didn't you just say "Fuck it, I'm not gonna ship this to you" to the winner?
I don't like to bring up the US law either. However, it can very well act as some sort "standards" guidance partially, in general, as standards and expectancies are what we're discussing here apparently.
The auction was ongoing when auctioneer bid, and is severely different from anything that would be done after the auction ends and against the auction rules.
So it's against auction rules to just refuse to sell to the highest bidder. But to do a functionally equivalent "fuck you" via self-bidding is ok? Come on now. Even in Finland that must be considered not cool.