It's a little more difficult to tell with DS games. Do you think you could post a picture of the cartridge, and maybe some screenshots? Perhaps screenshots of things in the game that you find odd, maybe? It's hard to tell when all you say is that it won't save. There could be other factors. I've heard cases of DS games getting run through the washer and drier by accident and not really being able to carry a save after that. Which, if that's the case, is why the previous owner sold it to GameStop most likely, lol.