My husband was a department manager at Walmart for Paper Goods, Chemicals, and Pets. They carried fish and trust me, he HATED it. Most of the fish came in bad shape from the supplier. Unfortunately it was not up to him who they ordered the fish from. But he did the best he could to care for them while they were in the store. Unfortunately, even that was difficult. Walmart is awful to their employees. (My husband works VERY hard and makes little money, less than $10/hr, as a MANAGER.) They expected so much from him, and unfortunately his other departments were more important to them than Pets. He had barely any help, either. He had one part-time associate who worked evenings, so he could barely communicate with him anyway. My husband cleaned the tanks first thing in the morning before they had many customers, but he didn't usually have time for more than a couple water changes, scrubbing the tank walls (they left the lights on in the tanks 24/7), and scooping out dead fish. He has since transferred to a smaller store that doesn't have a Pet department, and is desperately trying to get out of Walmart but in this economy we are just grateful that he has a job, period.
Anyway, sorry for the rant, but I just had to get that out there... if you want to complain to Walmart about the care of their fish, please don't take it out on the associates or the department managers. It's not their fault, as it isn't their decision to make and they are almost always being worked to the bone and are doing what they are told. Which is almost always to do something more "important" than take care of the fish. Take your concerns to the higher-ups: the store manager, or write a letter to corporate. Even then, I doubt they will do anything, since all the higher-ups really care about is sales :\
That being said, I believe that the best approach to this problem, any pet-care related problem really, is public education. If you see someone looking at the bettas/fish in general, explain fish care to them (if they'll let you, lol). Tell your friends about it. Heck, even explain it to the employees/sales associates if they seem to not know what they're doing ;D (most of the time, they don't. Especially at Walmart! I would hope that Petsmart/Petco would cover the basics in their training, but even then they are probably still swayed by what sells).
Bettas: "Ammo," lavender/cellophane SDeT male
and "Emo," black & white marble DeT male
... also two dogs, one cat, and one husband ;)