I had a similar situation with a gtp and Petco. I walked in and noticed it looking terrible laying in a very strange way. I told them about it and believe if I didn't actually tell them to open the cage and check it they would have gone about their business. I offered to adopt it and give it care but they decided to take it to a vet, which was great. While they were dragging their feet deciding who and how it would get there it died in my hands. I doubt I or a vet could have saved that one but they should have noticed days before it was not right.
Do not pay money for it. Try to adopt it and if that doesn't work report them. Its a sad situation but you just can not save every animal in need.