Not much you can do. If it's a big (all-in especially) raise, honor it and fold. If you find out he just had top pair, make a note of it and watch out for the same situation to come up again. My feeling is that they will have two pair or a set often enough that this fold is usually a good one; you need specific reasons to call. If the raise is more moderate, try re-raising them and see how they respond. A lot of players in 6 max want to think they're making great reads and they put you on overcards (AK is a popular favorite) every time you raise pre-flop. When they make top pair on a jack-high or ten-high board, they think they have you. If you spot this type of player, you're going to have to throw in some calls to make them understand that you don't always have AK when you raise. And if they don't push (leaving you wiggle room to re-raise), you need to use that tool. Make them understand that you mean it.