By policy the small animals get a varied diet. Lab block and seed mix daily. Can't remember the exact ratio, but I want to say 90/10. They also get veggies 3x per week. Used to have to buy them at the grocery store, but a few years ago I think they switched to the zilla dried veggie mix. Full clean out of display tanks once a week. Clean out of quarantine tanks 3 times a week. And clean out of sick tanks 3 times to daily as directed by the vet.
As for the snakes diet, when I worked there they had to be offered food every 5 days. We had to chart every snake feeding. If a snake went more then 3 feedings in a row without eating it went to the vet. At that point we were allowed to break the store policy on only feeding frozen thawed as it was under vet supervision. I had to go to another pet store to purchase live fuzzies from them to feed the snake. If the animal was not able to switch from live to frozen thawed it was then adopted out as a live feeder for free.
Believe it or not the actual written policies are not that bad when it comes to the care of their animals. Heck, even small animals that had little scratches and fight wounds went to the vet. Every time.
Now the issue is if the store is FOLLOWING the written policy. When looking at the snakes and thinking about purchasing - ask to see the feeding chart. If it looks like animals there are not being cared for - call the corporate number. They take complaints about the animal care in their stores seriously. Tell them that the animal looks thin and underweight. That will get the appropriate people checking those charts and getting critters to the vets.