I walk through three shops pretty regularly and look at all of the animals. While one of my BDs is from a local breeder and the other is adoption/rescue, I would buy a young BD from a "fresh batch" if they're not too small and there's no sand or loose substrate in the cage.
The very first key to successfully buying from a pet shop seems to lie in not asking any questions. Learn about what you're buying here, buy the right stuff mail order so you can get set up, then just go make your purchase, haul it on home and ask your questions here.
I have been told so many half-truths and outright incorrect statements by shop staff that I try not to discuss pets at all while I'm in there. Another problem is the UVB lamps they sell. The PetSmarts and the non-chain here all carry ReptiGlo, NOT ReptiSun, and will swear that the bulbs they stock are the best, while we know here that the ReptiGlo are ineffective and useless for this application. Best to know what you need, get it, and don't ask questions.
The list given above by sara24354 is great and I'd use it as a guide for picking an individual animal.
Anyway, I see many young BDs dumped into a small cage at two PetSmarts and the one non-chain fish & reptile place, and when they first arrive, they look pretty good. Alert, weight is good, eyes clear, no nips. Seems like the breeder gave them a fair start, and the only fault would be the tendency to get them sold a little too young. I believe they could be very healthy and happy if purchased that day or the next, and cared for properly.
All three stores only maintain a basking bulb over the overcrowded tank, and the leftover crickets I sometimes see running around the cages look a little large to me for such little baby lizards.
After being in the near-universal 10 gallon aquarium for a week or two, they seem to deteriorate pretty quickly, becoming dull and lethargic. The tank is too small, both for the number of denizens, and to have decent temperature gradient in case they don't feel like baking under the basking bulb.
I think the chances of success with these guys at this point is getting pretty low and best case they'll survive but are stunted. My guess is that by the time a couple weeks pass, they are becoming impacted, the lack of UVB is causing problems, they are too intimidated by the large number of cage mates to function, and/or they sorely need the
hydration of a good
bath. I'd also be suspicious of a parasitic problem due to the turnover of lizards in tanks that do not seem to change. I see buying one of these guys at that time more of a rescue than the act of picking a nice robust specimen/companion, and it's sometimes taking on a lot more trouble than necessary.
Adopting a real rescue is satisfying too, and kind of fun to see them pick up weight and change attitudes. Feels good too, to know you're providing a home for the needy and often helping the former owner through a tough decision at the same time. Nice to know your little buddy is going to a good home. I got a very nice normal adult male that had been passed along among several fosters. He was kind of bony and lazy when I got him and now he's plump and very active. He wasn't socialized very well, so he doesn't like to be handled and would not tolerate it, puffing up, hissing, lashing with his tail and trying to bite. I really can't blame anyone for not trying too handle him, he can be very intimidating and seems to know he could get his way with a good bluff. I take him out anyway, usually 2 or 3x daily and he has since learned to put up with me, sorta. When I come home, he runs over to the area where I pick up up, but then he remembers we're supposed to be fighting and resists being picked up, LOL. He'll come around at some point, and is an interesting challenge.