playing sheriff is a bad idea in these situations. Nothing good comes of it. Generally super obvious who the angle shooters are. Use the information for your self and if no one else knows the rules or sees what’s going on that’s their issue. If your not in the hand keep your mouth closed
There is an argument to be made that something good does come of it, outside of "policing the game" and discouraging angle-shooting - you get to see his hand!