I purchased bettas from this shop several years ago and all are still doing great. Part of the reason for this is the advice the staff gave and all the questions they answered when I first got my bettas.
The owner is a herpetologist and breeds his own leopard geckos. I have one and it was worth paying about $10 more to get him there than getting him at a large chain store because 1) his color is really beautiful 2) I know he was very well cared for.
This is not usually the cheapest place, but it's often not much more expensive than the big stores. I would rather support someone local when possible and these guys have been in Knoxville for about 20 years.