Lots of people seem to be forgetting the seller’s side, where you get tons of people who say “I’m on my way” and they never show up.
That’s why I never hold anything for anyone without a deposit. Nothing is sold until I have cash in hand.
As for everyone talking about “keeping your word” on a game that is massively underpriced, that’s just you being greedy and taking advantage of someone who doesn’t know any better. Don’t pretend there’s any virtue in “getting a good deal” like that.
In this situation, the OP is an asshole by offering over asking as a way to bully out other buyers, and then not offering a deposit. You can’t get pissy when the game is bought out from under you by someone who is closer.
That said this weird coin flip nonsense is definitely bullshit and I’d have just left when I was told someone else was in the running. Them’s the breaks.