I bought my Dumbledore (see avatar) from Walmart. He looked pitiful. I bought him before I even knew how to take care of a betta. I don't know what it was about him, but he just looked at me and said "Please help me...I can't do this much longer" So I gently picked him up and took him to the register. Best $3.45 ever spent. He went from one of those 1 liter bowls to a heater and filtered 3 gallon in 2 days once I read up on them. He's been my guinea pig and recently was upgraded to a 5.5, which was turned into a fully planted tank last night. He's a brat, but I wouldn't change him for the world. He's been fairly healthy ever since. Just a tad bit of fin rot after he chewed his tail into a double tail and then had a quick bought of internal infection of some kind but that cleared up in 2 days with Epsom salts.
Anyway, sorry for my tangent. I would never buy another fish from Walmart, as much as I want to. It only makes room on the shelf for another. They are all about profit and money. So, you buy fish from them, you support them. Even if you buy them because they are sick/dying. You still paid your money for them. :/