Sadly, to buy these guinea pigs would only then put more pigs in their poor, neglected condition. It would not change the behavior of the petstore.
It is good that you called the rescue that you have adopted from. You should also call animal control for that area as well as the state veterinarian. Most animal control does not monitor petstores. It usually falls under the office of the state veterinarian. Some will say that it does no good to call and complain as nothing will be done but it is still important to bring this sort of neglect to their attention. The more calls they receive the more likely that they will do something.
State Veterinarian List