Do you know any real-world examples of double-spends, where the second transaction was accepted to the block?
There's https://doublespend.cash/ for BCH but for BTC I would like some examples where the second transaction is accepted. (And this website shows all occurences of double-spends. I just want some successful ones.)
Yes, I did some double-spends playing on-chain games. It was years ago when a game (for example luckyb.it) accepted transaction with high-S-value, but most of pools did not include it into the block. The strategy was: send a bet with high-S-value, doublespend it if loss or wait several hours for a pool what confirm it on win.
As far as I remember, successful doublespend was performed by pool operator (I do not remember which one) when Bitcion forked in 2013 (0.7 to 0.8 version upgrade)
If it would be possible to doublespend bitcoin, it probably wouldn't have that much value as it have, right? But some of the wallets (BRD and Edge if I remember correctly) had this UI that portrayed unconfirmed transactions as already confirmed which led to some confusion of clients of these wallets and anectodal evidence shows that these wallet's clients might have lost money in the deal.
If you are looking for something closely related to bitcoin, but not bitcoin, I'd check the issues of (~2018) exploit of bad integration of Omni layer on the exchange. As some exchange (forgot the name) wasn't looking at omni layer status of verification (True/False for doublespends) but just payload of OP_RETURN script, it was possible to doublespend it, and this problem was found by some group of researchers.
