Walmart is where I just got my 55 gal setop about a month ago. Actually, it wasn't even a remote thought in my head to get back into tropical fishkeeping, but I was there for something else and saw a pallet of the setups marked $76. I though, dang! I cannot pass that deal up.
Turned out, an employee hadn't changed the sign and they were actually supposed to cost $160. But, as per store rules, they had to honor the mismarked price.
So far, I've had no problems but it's only been a month. I don't expect to have any issues with it, other than keeping an eye on the filter to make sure it does it's job well.
As for their fish, like phlawed said, it can be a hit or miss. I do have a 20gal setup in my sons' room with 2 goldfish that I got from there a little over 2 years ago. I haven't had a problem one with them yet. A betta, housed in a 3 gal, that I got from there about 3 years ago is doing great, too. Oh, the 10 gal setup came from Walmart. I forgot that. Same manufacturer of the tank, hood and filter as my new 55 gal, and I've not had a single problem with it in 2 years so that's a good sign, yes?
Back to the fish, my rule of thumb is to wait at least 3 days after they (any fish dealer, not just Walmart) have gotten new stock in before purchasing. If the fish are looking good and active 3+ days out from transport, chances are better that they are most likely healthy.
Lisa