Hope it works for you.
Buying a snake from a pet shop that isnt specializeing in them is a crap shoot at best. Ask to handle the snake first before buying check it over good, look for mite's , ticks , signs of an incomplete shed ect ect.
If it appears to be in good condition snap it up, Like you have said already youll be freeing it from its current fate.
Qaurentine it for sure and keep an eye on it for sickness.
Good luck i think your makeing the right decision.
Have a good one