I think they do get healthy animals...unfortunately, the employees are NOT trained well enough to be able to constantly maintain these animals on a day-to-day basis. In fact, I wouldn't even ask them about dog food. Most are not trained well enough to be giving ANY advice about ANY animal. My point was, that when animals are purchased through a pet store...all they're going to do is turn around and replace it with whatever they can, in the same horrific husbandry conditions.
I'm pretty sure that most of the time pet stores don't stock sick animals on purpose. I feel, however, that store employees could be trained a LOT better than they are. Most of the advice that is given out is to benefit the profit of the business.