But you don't know ahead of time who will cooperate, and who will cheat. The rule was "if you spend 1 coin, the other player gets 3 coins". If you change it to

But you don't know ahead of time who will cooperate, and who will cheat. The rule was "if you spend 1 coin, the other player gets 3 coins". If you change it to "if you spend 1 coin, the other player gets only 2 coins if they cheated", the game isn't fair anymore. Or am I misunderstanding something?