Hello!
If you find something that really bothers you at a Walmart store, don't yell at the workers. They're USUALLY doing the best they can with minimal staff.
The best thing to do is go to Customer Service and ask for a comments sheet to send to the head of Walmart. They have to give you one (although they might try to deter you from it). Fill it out and mail it in. If they're getting lots of complaints all about the same thing, they'll fix it. They'd rather fix the problem than loose you business.
I'm lucky I guess. The 'good' Walmart near me, has about 3 people that work in the fish department... who actually know about fish.
Their tanks have gravel, decorations, and plants. I've seen them medicating the hospital tanks (they separate the sick fish). As said previously, there may be 1 or 2 dead fish, but you'll see that in any petshop. If I see a fish I want at this store, I don't hesitate the slightest because I know these fish are taken care of (as best as possible in a store). The problem with most Walmart fish departments, is they have a tank maintainance company come in to do the water changes and water testing. And apparently, the company doesn't know anything about fish either!
If there's a certain fish you want, that's not extremely hard to get, ask if they can order it. The one worker at 'good' Walmart said they'd like to get different fish in, but they don't know what the customers want. That's why they stick to the everyday common livebearers, goldfish, and 'mixed' African cichlids (nothing against any of those).