I would agree with Shorin Ryuu, generally if a martial artist dose not know standard form that’s the biggest red flag. In relation to Nunchaku ask to see a simple demonstration judge, the speed, technique, and how clean the forum is. If he is sloppy then he most likely is not a great person to learn it from. Another way is to ask if you can see the 32 strike sequence he should know that if he is higher then 1st Dan.