I would like to buy fish that have been treated properly before being sold.
The first thing that jumps out at me is that obviously a bigger tank is better. One online resource I found essentially recommended a 10 gallon minimum for any fish. The pet store obviously does not follow this rule.
More generally, this seems like an uphill battle since I live in New York, where space of any kind is at such a premium that it's hard to imagine more space than is physically necessary being invested in selling a fish.
I don't think overcrowded fish for sale speaks well to their health or background or the care or concern of whatever breeder or corporation or farm happened to produce them.
How can I tell if a particular seller treats his fish well?