Mites can be common depending on the source of the snakes you purchase. Although I wont say all, many pet store snakes end up having mites, at the same time, I've purchased snakes from reptile shows and brought home mites as well. The best way to avoid this problem I've found is to make sure to check the breeder out with the BOI and always quarantine your snakes. As it's your first I'd soak the snake in lukewarm water for a while to get the mites off and when the PAM gets there clean out its tub/tank and follow the directions on the can to treat the tank. Always make sure to QT whenever you get any other snakes so that if this happens again the snake you currently have won't catch the mites as well.