I can't think of a worse philosophy to live by. If you think this way, where do you draw the line? At a sick animal in a pet store? How about a healthy animal that's simply living out its life in a tiny pet store cage? Or how about a pig that's living out its life in a spacious, clean pet store cage but that you just *know* would be happier at your house?I think there comes a time when the health and happiness of the animal has to over-ride our principles.
You can't bend principles when it's convenient for you.
I think this pet store fed you a lot of bull because their story (as you presented it) makes no sense. I think PM is right in that they are getting rid of their guinea pigs to make room for the bigger animals they intend to sell.
You didn't adopt or rescue - you made a purchase. Unfortunately there are now other animals living out their lives in this pet store.