While the video is of the supplier and is not indicative of in-store care, Petsmart has the option to sever ties with Rainbow at any time. Can't keep up the demand? Then stop selling guinea pigs altogether. Just as, "But he looked miserable and I wanted to save one" is no excuse for anyone here to buy a pig from a store, "We have to buy from that awful place to have enough to sell" is no excuse for pet stores to keep supporting the breeding mill misery.
The people at my local Petco and Petsmart all seem to care about animals, and I know the front line employees have no say. I do have one burr in my britches over Petsmart vs. Petco though. Our local Petco takes in dumped piggies, hamsters, etc. and adopts them out (minimal fee goes to charity fund, not to store, and you get all the equipment the animal was dumped with...it's how I got Quinn). None of the Petsmarts here do the same. I know they give the old "we can't mix adoption animals with sale animals" line, yet somehow Petco manages to do it. They just maintain a separate area for the adoption pets. While I can't be totally in favor of any pet store that sells any live animals at all, that makes them slightly better in my eyes.