I have two Walmarts that I go to on a regular basis. The closest one that I go to is just plain horrible. Always has dead fish in almost all the tanks, fish with ick, and gold fish tanks with what seems like 500 fish it them.
The other Walmart on the other hand has a great display of fish. Rarely do I see any dead or sick fish. Tanks are all clean and well kept.
I think what it boils down to is the people that work in that department. I don't know what kind of qualifications you need to work in the fish department or if Walmart trains these people. If you have an individual that is experienced in fish keeping and loves fish then you'll have happy healthy fish. Get an inexperienced person that is just there for a paycheck then you have mess.
That's my opinion. I've bought lots of healthy fish from Walmart. Just be carefull what you buy.