They most certainly are a thing, but typically a general pet store (or any large corporation IMO) will treat the fish just as another product on the shelf.

A reputable store will

1. Know a lot about the specific fish and the hobby in general.
2. Know where the fish come from (ie wild caught or captive bred).
3. The tanks will appear in good shape and the fish will appear active/healthy. New arrivals will be stressed out from shipment, but any fish that has been in for a few days should be adjusting. Also, some fish just get sick. This should be addressed and not silently dying in the corner.

• However, if I see saltwater tanks with cyano, excessive algae, gasping or sickly fish, etc; I won't buy even the healthiest looking one of the lot. They should also be willing to feed it in front of you to prove this.

4. The store will try not to just sell you a fish that you can't handle or isn't compatible with your setup. Everyone I deal with actually cares if the fish lives when you take it home.

This is by no means an exhaustive list. To address your overcrowding concern: Yes everyone said about large filters but something missing was most fish stores have a large communal body of water shared amongst the tanks. Think about having a large tank as apposed to several smaller ones (adding up to the same volume) and piping them together. The bigger difference in the latter case is ensuring the fish have enough room to be happy/healthy. But then again, this is hopefully a short term home for the fish.

They most certainly are a thing, but typically a general pet store (or any large corporation IMO) will treat the fish just as another product on the shelf.

A reputable store will

1. Know a lot about the specific fish and the hobby in general.
2. Know where the fish come from (ie wild caught or captive bred).
3. The tanks will appear in good shape and the fish will appear active/healthy. New arrivals will be stressed out from shipment, but any fish that has been in for a few days should be adjusting. Also, some fish just get sick. This should be addressed and not silently dying in the corner.

• However, if I see saltwater tanks with cyano, excessive algae, gasping or sickly fish, etc; I won't buy even the healthiest looking one of the lot. They should also be willing to feed it in front of you to prove this.

4. The store will try not to just sell you a fish that you can't handle or isn't compatible with your setup. Everyone I deal with actually cares if the fish lives when you take it home.

This is by no means an exhaustive list. To address your overcrowding concern: Yes everyone said about large filters but something missing was most fish stores have a large communal body of water shared amongst the tanks. Think about having a large tank as apposed to several smaller ones (adding up to the same volume) and piping them together. There are of course other factors to consider in what constitutes a proper setup, but that would turn this answer into a book.

The bigger difference in the latter case is ensuring the fish have enough room to be happy/healthy. But then again, this is hopefully a short term home for the fish.