> There are no indications so far that the successful punters have had to return their winnings. However, the data source for Paris’s hottest temperature has since moved to a sensor at the smaller Paris-Le Bourget airport. Here's the negative externality that no one will care about. There's no reason gamblers won't repeat this stunt, until us poor schmucks who just want an accurate temperature reading have to build a…
Usually the TOS of these betting markets prohibits tampering. IIRC, someone bet on a streaker at the super bowl, did the streaking themselves, made 6-figures on the bet, bragged about it publicly, and the market negated the bet and recovered the money.
Ultimately they don't care too much about this kind of tampering, except when it has the potential to damage their reputation. They otherwise don't care about the specific outcome of a bet; they make their money regardless.