A live mouse pinky - heck even a live rat pinky - is too small of a feeder for a baby ball python. Given this one's age it was probably eating either live mouse hoppers or rat fuzzies when the breeder sold it. Most breeders don't bother converting their babies to f/t.

As for the store, if the owner is keeping the babies in a tank and then moving them to eat during daylight hours, it's a good bet those babies won't eat. Typically they eat at dusk and they want to be well-settled in a small, dark, tight, private place before the feeder shows up. This is why BP's don't thrive in a retail environment - stores and displays are brightly lit, and the displays don't give snakes a place to hide as otherwise customers couldn't see them.