My Petco is alright compared to the others. The employees are at least somewhat knowledgeable in fishkeeping, some are even
too picky in letting people buy fish. Once I tried to buy an angelfish, the guy asked what I had in my tank. The tank I intended to put it in was my 55 gallon community with some tetras and platies, yet the employee didn't let me. He said, "Platies require different pH than angels." I do have soft water at around 6, but I've bred platies numerous times in that water! I didn't want to argue so I left.
The local Petco's tanks are okay, but there are times where you see dead fish in the tanks. I once bought two banjo cats. As the employee went to catch one, we found it was dead
Petsmart is similar, though the tanks are larger and there are more selection of FW fish. The problem with Petsmart is some of the labels for the fish are inaccurate.
Red-Bellied Pacus apparently have a minimum tank size of "75 gallons"! Balas, Clown Loaches and Tinfoils need a "40 gallon minimum", and Pangasius need a "75 gallon minimum". Terrible advise, I can imagine people buying a group of Pangasius and a trio of Pacus for their 100 gallon!
Also, another bad thing about my Petsmart, they sell Columbian Catfish (Arius jordani), without making sure people know they are brackish water fish.