that's interesting, because i've actually had some good experiences with our local petco. i'm assuming they differ, nationwide, just like any chain store does. i have three friends who work at this petco, and they're all conscientious people. they host a cat rescue group every weekend, which brings in adoptable cats and sells pet treats and toys as a fundraiser. in addition, our petco often recommends that people looking for pets adopt some of the abandoned rats/mice/hamsters. i went in looking for something else, but for a $5 "adoption fee", i got skunk and her friend squirrel (no longer with us) AND their 16"x16"x24" cage.
also, i had one situation where a friend of mine bought two baby rats from petco. within a week, one died unexpectedly and suddenly, and then the other started showing respiratory symptoms. my friend (we had some harsh words over what happened next) "returned" the rats and bought new ones. i was afraid for what might happen to the little one he returned if it seemed like no one cared about her, so i kept calling petco to ask about her and coming in to hold her, and i told them i intended to take her home if she made it. she didn't survive, but i now have a lot more confidence in the competence of this particular petco, since they spent almost two weeks giving her oral and topical antibiotics. they should never have been selling them this young in the first place- i'd guess maybe four weeks, but probably younger. still, the employees, if not the owners, did a good job in this case.
...sorry this has been such a long reply.