I've played 1882 rated games and today for the first time I encountered "undo abuse" --- I was winning against a much higher rated player (dominionfan458), they requested an undo, I reflexively granted it because I always do, but their undo rolled back to the start of the game :-(.
This seems grossly unfair. Of course I'll block them, but is there something else that could be done, e.g. prevent undos that want to replay entire games?