You have a delicate downhill 6-footer for par but you note two pretty large spike marks in your line. A fellow competitor putts first and his ball ends up on your line but only three feet from the hole. He stares at his ball and you sense he is about to smash down those two spike marks. The thought crosses your mind that flattening those spike marks will make your putt a lot easier. As you are pondering whether to warn him about not fixing spike marks he smashes the spike marks and rolls in his putt.
Do you accept a 2-stroke penalty and advise him to add 2 to his score? Or do you consider your delay in warning the other player to not have risen to the level of tacit approval of his actions?