I'm sure there are some acceptable chins in pet stores but I still think you would be hard pressed to find the next GSC there.
Oh, you would be surprised. Ask the JAGS about their GSC pet store chin that they pretty much started their herd with. I've seen some awfully nice animals come out of pet stores.
The large ranchers are culling these chins for a reason whether it be size, fur, genetics, ect.
This is what I struggle to explain over and over again. No, they are not "culling" these animals. The culled animals go to research. Most wholesalers will not accept adults. They want babies. Babies sell, adults don't. They have a contract that needs filled. They go to a rancher and say "I need X amount of chins." The rancher goes down the aisles and starts pulling out babies. They pull them at anywhere from 6 weeks to 3 months. As you know yourself, there is absolutely no way to know what a chin is going to be at 3 months of age or younger. They have a contract to fill, as does the wholesaler, so they send what they have. I have heard more than one person who sells to wholesale comment that they probably shouldn't have let "that" one go, but that they needed to in order to fullfill a contract.
So yes, it is very possible that the next GSC has been sold many times over through pet stores.