Oh wow... that's horrible! I'm sorry for your loss What kind of person sells a snake showing signs of illness.. Not cool at all. Definitely make sure to get every penny back from this person.

If I were you, I would continue to tweak the set up until you're confident it's perfect, and then purchase a snake from a breeder with a good reputation. If you're looking for a normal BP, they are very, very affordable even including the cost of shipping. From what I've seen thus far, breeders will sell them for less than most pet stores.