Sorry! I forgot to add that it doesn't apply to all pet stores. Some take really good care of their snakes. Just I've heard that some big box stores like Petco, Petsmart, Pet Land etc have protocols for snake care that you can't change even if you work there and see it's wrong. I've heard stories of snakes that could eat again if the husbandry was adjusted, but are assist fed because they can't break enclosure protocol. I've heard a lot of cases like this but I guess I can't confirm so I could be wrong.
Not all pet stores of course, it always depends on location. Some pet stores I've been to have great looking reptiles with nice and clean enclosures. Other pet stores, I have definetly seen some poor snakes with stuck shed, species being cohabbed that shouldn't be, dirty tanks etc. As I said it always depends on location.
Just in my experience I personally wouldn't recommend a BP from a big box pet store to a new keeper unless I knew for certain that it was eating well and had no problems. A high-quality, good eater is less likely to stress a new keeper out, and at a pet store you might not be able to find out the animal's history, genetics, and habits.
But you're right, I shouldn't make complete generalisations. Not all pet stores are bad, not all breeders are good. Just make sure wherever you get your snake from that it's healthy and eating, especially if you're a new keeper.