I shop at Petsmart. I have a PetCo close by, but even though its also clean, prices are higher and they don't have the selection.
I've bought plenty of fish at Petsmart. I used to be a Petcare Lead there. I know how to pick healthy fish. I've bought Otos, Neons, etc.
my last female Harlequin Rasbora refuses to die
She is at least 5 or 6 years old and has survived moving, living without a filter, etc. she is the queen of my rimless 10g and Im hoping to rehome her to a club member's 55g with a big group of HR. Her last male passed away recently. He was also at least 5. I know they can go 5-7 yrs. my Petsmart isn't perfect, but they do try.
I'm lucky to have several LFSs within an hour.
AquaForest in San Francisco is tiny but has ADA equipment and lovely tanks.
For Nano fish I trek down to Neptune's in Milpitas CA. Tiny store on a strip mall. They have SW, but they have plants , ADA retailer as well , plus a great selection of uncommon FW including Nano species.
http://www.neptuneaquatics.com/catalog/fishes/tropical-fish
So there is no way to say overall Petsmart or Petco is better than the other. And Ive seen plenty of Mom and Pop stores I will never buy from. It's a nice theory that they must be better, most can't afford to hire enough help and their fish suffer because of it.
You need to remember, the general public doesn't always notice things. Or they might believe flimsy excuses for why there are dead or dying fish. Just because a store is around a long time doesn't mean it's a good store.
Any store will have dead fish. Good stores, pull deceased, record it and figure out what's up if there are large numbers. Good stores try to prevent disease, treat the fish if needed and its possible or refuse a sale if the fish aren't healthy.
There will always be some loss, keeping it to a minimum and helping customers' fish thrive is the goal.
And in San Francisco in an alley is a true M&P store. Looks very cluttered and claustrophobic.
Plants overgrown in every tank. Homemade CO2.
Lots of tanks you can hardly see the fish.
BUT unless you bring a water sample and convince the owner you have the right tank, he WON'T sell you a fish. He has the best Bettas Ive ever seen in a store. His fish are fat and sassy. He has tanks of Guppies all over, all different color strains. His selection beyond Livebearers is limited, but still a cool store to visit !!
But between the sketchy neighborhood and the alley and the first impression, I never would have stayed except my club member told me it was better than it looked.