I got my first BP from a pet store and she is doing great. It sounds like you should be fine getting this snake. Chances are everything will work out fine just make sure you handle the snake and look for mites/signs of Respiratory Infection. Also look carefully at the enclosure the snake is kept in: is it dirty? The cleanliness of the enclosure can show how well the guys that run the shop take care of their snakes.

If you decide to find another ball i would suggest buying one from a breeder directly.

Here are a few well known breeders:

http://www.jkobylkareptiles.com/index.php

http://www.ralphdavisreptiles.com/

http://pythonregius.com/

You really couldn't go wrong with any of these guys; and remember if you don't see anything you like on their websites just contact them and ask if they have what you are looking for. These guys have hundreds if not thousands of Ball Pythons so chances are they have one that's just what you are looking for.