[Ranma4703]

The K is a great card to bluff, if you are going to fire the turn it is the second best card to bluff on. However, your hand has showdown value and getting c/r'd would suck. I don't think you fold a 9, so the reason to bet the K would be to charge a straight draw like JT, which is drawing to 10 outs vs you if he has no hearts. You could also bet to reduce the chance of him bluffing a whiffed flush/straight draw on the river. Against an unknown, betting makes your river decision a lot easier vs a bet, and builds a pot for when you hit, and only really sucks when he check/raises the turn, which he is only doing with a poorly played set or two pair, so I think you should bet the turn, but it is so close it doesn't really matter that much.