In this scenerio, there is no way to know what your opponent has, because he only called your bets. He never told you that he was leading because he didn't raise.

A set is by far the most difficult hand to put someone one, because sets are generally slowplayed like the example you posted. The best way to find them is to have your opponent bet or raise you. This is where dicipline comes into play when you have TPTK or an over pair.If you are getting raised prior to the river, you might be loosing with your pair of aces.

It all depends on what level though. I have found that the lower the limit, the more set slowplaying there is.