You can't rip on the whole chain because one store is inadequate. There are plenty of petsmarts, petcos, etc that are wonderful stores, well maintained, knowledgeably staffed, and sell healthy animals/fish. Then there are others.
Trust me when I say that Petsmart doesn't want you to come into their store and see dying and diseased fish. If you make a complaint to a manager and they are not polite to you and give you a solution to the situation, I highly suggest calling corporate. You should be able to find the contact info on their website. Give the detailed information of what was happening, where you were (store location) and I'm sure something will be done. Whether it takes one try or several is another thing, but in time, the situation should get better.
Also, please remember that Petsmart/Petco have certain policies they must follow as opposed to your local family run pet store.