I've bought many fish from the PetSmart and a few from MrPets near me. They take good general care of their animals, and the staff i run into do seem to genuinley care, even if they've been ill-educated.
The Mr.Pets in my area is very small, and makes a real effort to employ people with hands-on experience with each type of animal. They used to employ a young autistic man who had a vast knowledge of fish. I know this because he and I used to "hang out" in the store and I would watch and learn/help him as he cleaned tanks and balanced water. They currently employ a young man who owns various reptiles (mostly snakes) and he has an excellent knowledge of reptile care, even if the store hasnt provided quite the right lights in the temporary enclosures. They even take good care of their crickets!! I always get them there, because if I get them anywhere else they smell awful and are covered in their own poo! Ick!!
I'm less-than-impressed with the PetCeteras in my area.
They have a tendency to overstock, not listen to friendly advice, don't employ knowledgable staff, and many of their animals (especially birds and reptiles, I've noticed) are agressive.