I would never in a million years buy fish at Walmart, because you're right: their only objective is to sell as much as they can and make profit. It's a large company that doesn't have time to care for much such as fish. I mean, they don't even care for their employees that work there, so why would they care for fish, right? *burn*
In the past, I did buy a fish at Walmart. I was probably about 8 years old and I had wanted a fish to take care of after my first cat had passed away. My mother thought it would be a good idea and to be honest, fish weren't that hard to take care of. I looked at all the fish that Walmart had to offer and I chose one. It was an Angel Fish and I thought it to be the most beautiful fish that I've ever seen. We took it home with our brand new fish tank set and within hours, the fish had died because it was sick. The hours before, it would cause discoloring to the water and often had a weird string come out of it from behind. We never knew what it was, but we knew that the fish wasn't going to make it and my mother was disappointed.
So now, when I go to Walmart, it is only for their pet products (because they are significantly cheaper), but never will I buy another fish or any animal from them. If Walmart ever did sell animals such as dogs, cats, and more, I would probably fight against that and make sure that they are taken to a better and well-trained corporation.