KK makes an easy river fold

I don't see how this is an easy fold. The pot is large enough that you only need to win this pot 1 out of 12 times for this to be a profitable call. You don't have much information on this player, so you really can't be more than 90% certain you are beat. Some weaker players may play a hand like AQ this strong. Call the check raise on the turn and call the river.