I never buy fish from anywhere that looks unkempt or where there appears to be something that died from disease. There are about 5 Petsmart locations I go to often, one really stands out in how dirty the tanks are, and the number of dead fish, especially ones that look to have been sitting awhile.
But buying from a place free of dead fish is impossible.
True, fish can die relatively easily, and if you have a hundred or more tanks, there will certainly be causalities.
Everyone should be rational enough to understand that, what I can not for the life of me fathom is why some lfs's will leave the dead fish in the tanks!!!??
There is one store that ALWAYS has dead or diseased fish in their tanks, which is a real shame because he has had some awesome saltwater fish, but I will never buy any fish from his tanks.
Now the part the irritates the worst is the owner at times will lament about how slow business is and "woe is me", the whole time I'm thinking
"If you got off your butt and took the dead fish out, you might sell more."
Eons ago when I managed a lfs, we would walk the store every hour checking the tanks for sick or dead fish. It really isn't that difficult, don't know why all stores don't do it, and it does have a direct impact on the bottom line.
There is absolutely nothing more embarrassing than to have a customer point out dead fish in the tanks.
Concerning your local Petsmart with nasty tanks, just call their corporate office and tell them their merchandise is dying (literally) on the shelf and profits are literally being flushed down the toilet.
If you call and complain about the poor fish and how terrible it is for them, nothing will happen.
If you call and tell them they are losing $$$ daily because of poor upkeep of the department, someone will be looking for a new job and that Petsmart will be looking for a new "fish guy".