At the moment I'm an overnight stocker at a Wal-Mart, and the place where I was assigned to work was Pets. Now, I'm very much new at this (My just bought my tank about a week ago, and its currently cycling (fishless) Any knowledge of fish (or pets) in general wasn't a necessity for this job. Granted, I'm a overnight stocker, so there really isn't that many people coming to buy fish from 10PM-7AM.
However, I do sell probally 5-10 fish a week during those hours. I try to be helpful with customers, but for the most part my knowledge is limited to whats on the cards. If a customer comes in and says I want one of these, one of theses, and one of these, thats what I give them. I "hope" that they know more than I do about the fish they are buying, but if I do ask them any questions like "How big is your tank" and they say, "oh, its pretty big" I kinda guess that they don't. Generally they buy guppies or swordtails or other fish that will probally do OK in any reasonable size tank.
I think it would be nice if the people who worked in the daytime knew about the products they are selling, but, its Wal-Mart. Most people who are knowledable about fish aren't going to work for less than $8.00/hr.
I think the big thing regarding the tanks at Wal-Mart is the manager in charge of the pets dept. A good manager would keep the tanks in decent shape, and if you have a problem with something at your store, I'd bring it up with that manager (as they may not even know the tanks are in bad shape), and if it doesn't improve, see the store manager. The store mananger, more than likely hasn't a clue about fish, the condition they are in, however, he does know that bad fish tanks aren't good for the stores public image, which it tries hard to keep as high as possible.
I had a customer come in the other night who told me to tell the manager that the tanks were looking a lot better than they did last time she was there, so if there is something you see that is wrong, let them know. Most of the employees really don't know all that much about the products they are selling.
The store I work at does $80,000+ of sales a day. Last year it was about $120000 but they opened a new one 5 miles down the road so sales are down a bit. If we sold $250 worth of fish a day that would be 0.3% of total sales. And I doubt we sale that much. So, Wal-Mart could stop selling fish and it wouldn't impact revenue very much, but, at the same there, there are a lot of places in the South were a Wal-Mart is the only place to get fish.
Bottom line is there are going to be good fish tanks at some Wal-Marts, and disgraceful ones at others. Sorry for such a long winded post, but I, for some reason, felt the need to fully respond to a lot of things said.
I want to make this one point clear though. If the fish tanks at your local wal-mart look bad, do something, complain to the manager of the dept. and to the store manager if that doesn't work. And, if that doesn't work, go higher. Trust me, the corporation doesn't want their stores to have terrible tanks.