Petco is a huge pet store chain in the U.S. with over 1000 locations. Each one is slightly different from another. I have seen the selection of fish at one store to be zero as all the tanks are empty because of "remodeling" to all the tanks are full, clean, and have a very good selection of healthy tropical fish!
Some of their stores have excellent and enthusiastic (fish) department managers and some others do not. This particular Petco at 200 S. La Brea in Los Angeles, California is very well run and clean. Their selection of well priced hard goods is very comprehensive and often very low priced. Need a filter cartridge for your aquarium filter or fish food? I guarantee most Petco stores will not only have it but have 10-20 of them if you need them, and this location is no exception.
Fish selection is very good if you like small to medium sized fish, but not very comprehensive for the rarer species. One of the cool things about Petco is that they will often have seasonal fish of very good quality and cheap! The collecting season in S. American is during the Winter and Spring for N. America and Europe. Tetras, Corydoras, and live bearers of all kinds are often very cheaply priced.
Often times employees are not well trained on the different types of fish. If one was so inclined you can buy some African Cichlids for less than the posted price because they don't know what they are looking at! If you want to stock a child's aquarium or a nice community aquarium that is a different matter, and Petco is a good choice.
This Petco has a nice fish department, but was understaffed when I was there. People were standing around waiting to be helped with no one in the fish department to help them. I have been in fish stores (not many!) where I have been trusted to catch and bag my own fish, and if I had wanted a fish on this trip I might have been tempted to get my own! As it was, it was an expedition to buy chloramine remover as I wanted to do a water change and I had run out. No problem buying it at this Petco! Would I go back? For fish supplies, yes. For fish? I would, but I would not wait longer than 10 minutes to be helped. Call ahead for reservations maybe??