As a veterinary technician, I too often see cases of animals purchased from pet stores who are ill, or who are born with congenital diseases because of poor breeding, especially with animals who are purchased from puppy mills  Inbreeding in these mills produces animals with serious conditions.  

I firmly believe, first and foremost, that pet stores SHOULD NOT sell animals, but if they are allowed to continue in this practice, there MUST be stringent regulations put in place so that animals are not suffering and consumers are not stuck with pets which will require a good deal of medical attention.