it doesn't mean that you will know immediately whether he is playing or not by any means! There is no such way unless you judge for yourself! You should be prepared to be played first, which means you should play with him first! When you feel that you can have fun, just do it at your discretion! People play with you, you play with people, and if people don't play with you, you have to try this kind "playing with people" and hurting people. There is no reason why you can't be defensive!