Oh, thank goodness the man had the heart to take the snake out of it's horrid environment! And thank goodness that he found such a kind-hearted person to take it in after him! It sounds like you're quite committed to the snake, even prior to owning it. That's very reassurring, and I am willing to bet that your new Ball Python is already very greatful to have met you!

Have you taken him to a vet yet? I would highly recommend it, especially considering the mites. He may have also had some internal issues as well that you should look into.

Good luck, and post some pictures!!!