Depending on what state you are in, you could see if animal control would be willing to press neglect / abuse charges. Also try the humane society, and USDA under the animal welfare act. Keep the pictures as evidence, including the for sale sign. Sometimes they can get away with having obviously sick animals if there is a "not for sale" sign on the tank. You could also try calling your district attorney, they may be able to direct you to someone with legal powers. Another way to get the word out if your really up for a fight is to call your local news, if they have a community section of their daily programs. Too many time I see things like this in my local pet stores, but in VA it's nearly impossible to get anything done about animal abuse.

I love my ball and have no problem with people having them (as long as they know how to care for them), but this is the precise reason that I believe that exotics should be illegal to sell through these chain stores by people who have no knowledge of care and health. Most of these stores will sell anything to anyone and never ask if the person knows how to care for it or the employee's are trained to make a sale and often either make stuff up or give the worst advice, and the majority of them couldn't tell a goldfish from a hermit crab. I have argued with the managers and store owners, employees, and every time have been met with stupidity (I am referring to the unwillingness to listen to someone trying to teach you and refusing to admit that maybe, just maybe, corporate on the job "training" does not make you qualified in animal care). I have pointed out obvious signs of ill-health and usually the answer is either, 'I'll let someone know' or "Oh, I didn't see that. I'm sure it's fine" or some other platitude. Yes, there are some employees out there that go home and actually learn about the animals under their care and are responsible when working at these stores, but the vast majority are not like that, at least in my experience. Because of this, I rarely go into any pet store, and when I do, I usually see or hear something that makes me super frustrated and angry.