I play World Tavern Poker at a local bar here in town. Last year we had an incident with a husband/wife cheating team. They had a code system with at least a few ploys. One was where they would either use each other to bet up the pot to give someone pot odds for calling against one of their monsters. Another one was when one of them would get the other to fold so the first one could take the pot, either to transfer chips or to prevent playing against each other. It was suspected for a long time but it's hard to prove it. One time the dealer (we take turns dealing) "accidentally" flipped up the folders cards and showed that she had folded the nuts, but she said that she didn't realize she had made the straight.

Finally, the TD told them "I want you to know that every single person in this group is going to be watching both of you every second of every tournament, looking for any sign of cheating. If you're not cheating, then you have nothing to worry about and are welcome to continue to play with us. If you are cheating, we will catch you and you'll be banned from all tavern poker."

They never came back after that.