Sorry you had to deal with that! Just a quick idea though, if their snakes were ill with anything the mites could have spread certain illnesses to your snake after feeding on theirs, so I would keep an eye on your snake and watch for any symptoms and keep him quarantined from all your other reptiles. They sound like such shoddy reptile keepers that I would not be surprised if their animals were rife with disease, it would be a shame for something else to get spread to your own collection. Good luck!