I did some research in dumping damaged dvds lately because I had some little treasures laying around that were just unusable.
I had good success using DVD Decrypter (hardly available, I got my copy years ago) ignoring bad sectors in the settings, Redumper[1] and, if DVD is only scratched very badly using car-anti-scratch / polish chemicals with a lot of patience [2] (some hints: Toothpaste does not work unless it is whitening toothpaste, don't use tools like a drill, will make the problems even worse, prefer the slow process of polishing by hand).