I have several Petsmarts and Petcos in the vicinity, and they are all very different. The staff also varies widely, even within the same stores. The last time I was at one of the Petcos, the guy I dealt with was outright rude. Whereas I wouldn't hesitate to buy fish from one of the Petsmarts, I wouldn't touch the ones from the other one.
On the other hand, all this is also true for the non-chain fish stores. Some of them suck, others are great. I haven't really met a store where I'd say that this is the one I'm happy with and stick with. On the other hand, my insight isn't very deep yet, so time will tell .
The Petco down the street from me is simply where I buy my supplies. I've only picked up mollies and cories there and don't ask any questions. The Petsmart only a few more miles away is excellent. A girl maybe about the age of 18 was netting the fish and seemed to have a decent amount of information for the customer.
Now, the Petco in the town next to mine I find very amusing. I was looking at the bettas, mostly pitying their existence and one of the employees came over, an older lady. She began patronizing me and asking me if I had ever had one. I stated that most hobbyists do start with a betta, so yes, I've had my fair share. Then mentioned how I had some other fish and I don't think she considered me an ignorant child anymore. I think they really like me there. Bettas are the only live animal they sell there, but I come mostly for their plant selection.
every now and then mine gets some nice anubias plants. I've bought lots of them for 3.99, which I considered a bagain given their size and quality. I wouldn't buy anything else from that store, including supplies which are expensive.
Since I can sterilize plants, I buy them from chains. Everything else is pretty much guaranteed to bring in disease. Those flow-through tanks are notorious for spreading stuff around. But as others have said, each franchise is different. There is a Wal-Mart a few hours away with a really nice fish department, believe it or not. I think it all depends on the management.
my petco and petsmarts are fine. my LPS are horrible. i actually really like my petcos and petsmarts. a few dead fish in a tank is not a big deal at a pet store. they usually go around every morning and remove the dead ones, but some might die during the day when all the employees are around helping customers. anyone who has mailordered fish knows that they don't all live. no matter how perfect their tank was at the supplier, or how perfect yours is, some just don't make it. the same goes with pet stores. they get their fish in the mail from a wholesaler, and not all of them make it. seeing dead fish is not the end of the world, though i agree there shouldn't be a LOT of them.
the reason that those stores don't take care of their stuff as good as private owned is because they just hire people of the street without any expirience because they don't want to pay anything more than minimum wage. so it comes down to frenchised stores having those sections, but not the right people to take care of them. but if the private owned stores are no good then it's the owners to blame, because they there all the time.