First off, who said the OP wanted to switch the snake to F/T? Second, wrong! We have NO clue what the husbandry is like in this BP's current situation. There is a very high likelihood that the current owner is a ding bat and has now idea how to take care of a Ball Python. It could be going off feed in the winter because the current owner can't, or won't keep the proper temp range in the enclosure.
To the OP, while I'm not a huge fan of rehoming snakes from Craigslist, if you do chose to take on this BP, there is no reason that with proper husbandry that the animal won't make a fine pet.