Either way, the only “pets” you should ever consider buying from a store would be things like gheckos or hamsters. Dogs and cats should only be bought from reputable breeders (verify from a good vet that the breeder is a reputable breeder and not just a back yard breeder akin to puppy mills) or adopted from shelters or rescue organizations.
When you buy a dog or cat from a pet store, you are buying an animal that was bred in a puppy mill or its feline equivalent. The breed registration papers for that animal might be valid, but they do not ensure that you are getting a healthy or quality stock animal.
You are correct....and obviously use the common sense God gave you. ;-)