Also if you see little black specks and suspect they're mites, just poke them hard with your fingernail and they'll move. Anything else that isn't mites won't move.

A few months ago, I saw a black speck on my GTP's face and someone told me to just pick it off and see if it moves. That's the sure way! LOL
(it wasn't mites, it was a speck of dirt)