I can tell you why pet stores such as these shouldn't be supported, from just today.
I went in to PetSmart to check the small animals (I regularly do) and found the two male pigs to be quite ill, crusty eyes and nose, not moving, labored breathing, classic symptoms of a URI.
I pointed this out to the manager, making sure other customers and employees heard me, and was disgusted to learn that they are indeed well aware of the problem and not only that, but they have another pig who is even worse off "in the back" that they won't put in the "showroom" because he "won't sell" and "puts customers off."
I asked what they were doing for the pigs, and the manager informed me that their onsite vets (Banfield) were "checking on them" four times a day and that they'd been treated repeatedly but nothing's helping. I asked if they were getting an antibiotic and he said, nah, no need, it's just conjunctivitis. I told him they need to be on an antibiotic, nothing penicillin based, and he blew me off, so I went to talk to the Banfield folks, who explained, again, that the pigs just have conjunctivitis and not to worry. I explained to the "small animal specialist" that these pigs were very sick and would die without antibiotics, and that the antibiotics needed to be cavy safe, something like Baytril. The man guffawed and said Baytril was "too expensive" to give a "guinea pig."
I was then essentially told I could buy the pigs and take them to a vet of my choosing or get out.
I'll be calling back in the morning, when presumably someone else will be there, and hopefully I can get them to contact my vet, who is very experienced with small animals, for assistance.
After having this experience, I'm not sure why anyone would be inspired to go and buy a guinea pig or other small animals from such uncaring and irresponsible people and corporations, yet somehow there still are. Wonderful.