Any one of the chain petstores will vary as far as fish quality...since each store depends on the quality of knowledge of the one who is responsible for the fish section of the store.
I find the fish at my local PetCo are pretty good and their tanks are impeccably cared for...and I always make sure to comment on that when I go there. When they do such a good job keeping things clean and tidy, they deserve a compliment.
The PetSmart on the other hand...I would say is..so so....much better than walmart..(which isn't saying much)..but not as good as PetCo. They're tanks aren't as clean and attractive..and I usually see the gouramis have stringy poops..and there's plenty of 'stuff' in the gravel in the tanks..meaning, they don't get vacumned very much I figure.
I imagine it's always best to get fish from a fish specific store if you have one nearby...but they will generally be more expensive.
One thing to keep in mind when buying fish from a large chain is that what the label on the tank says may not actually be what is in the tank...and the employees may or may not know either. Be sure you can positively ID a fish before you buy it, or you risk not getting what you pay for.
I have purchased some fish from large chains, but I prefer to get cichlids right from the breeder (usually via the internet) as the selection and quality are almost always better.
When buying from the large chains it is critical to quarantine your fish. As was previously stated, places like Petsmart do run the same water through all tanks. They usually have a UV sterilizer, but it is not enough to kill all pathogens, so quarantine your fish for a few weeks before adding to the main tank and you should be ok buying from Petsmart or petco.
the best thing you can do is take a good look at the fish. Are then any dead ones in the tank? If so, then move along!
The good thing about Petsmart is that they have a 14 day garuntee. Also, young cichlids living for 10 months or less isn't all that uncommon. The chances of them reaching adulthood are slim and not necessarily due ot the vendor.
In my opinion, Petsmart does have reasonable prices. At least they are the best priced around here as far as fish go.
I bought my cichlids from Petsmart. The prices were good, they had a 14 day guarantee, and I was fortunate to have a manager help me who had raised cichlids for years. The selection was pretty good - they had about a dozen varieties plus the 'mixed cichlids we-aren't-sure what they are tank.' So far so good, although I've only had them for 2 weeks. All look healthy so far.