From a couple of weeks ago, but probably worth knowing about: https://www.timesofisrael.com/gamblers-trying-to-win-a-bet-on-polymarket-are-vowing-to-kill-me-if-i-dont-rewrite-an-iran-missile-story/

tl;dr -- it sounds like organized crime (or perhaps just would-be gangsters and sore losers) have discovered #Polymarket, and are handling losing bets exactly as civilly as you would expect...