ok, it start to make sense. I double-checked for how long it has been around (nearly 10y) before sharing it here. I assumed some cryptography expert would be interested.

After all, even if built with the best intention, this marketplace is selling bets... gambling by principle. And in fact, as you mention, a buyer will be never able to verify true ownership of the wallet.dat. Thus yes, this site could be selling stolen wallets.