A casino or bookmaker doesn't need to heuristically identify betting behaviour that's 'smart'. They don't need to spot evidence that could be hidden by good opsec. No need to find micro-expressions or hidden cheating gadgets. Nor to do background checks to know you've got a buddy with insider knowledge.

All they need to do is check if you're cashing out more chips than you came in with.

It's not trivial for the casino to track this against a determined adversary. If you're already thinking about "good opsec", you can get someone else to help cash out your winnings.

A buddy from out of town, or a losing regular, or a poker player who the casino doesn't care if they win. In Vegas some casinos' chips are negotiable, officially or unofficially, in other casinos.