BenQ 1620 drives are known to be good readers and I've used some scratched dvds in mine with few problems, but if the scratch goes round and round the disk, it may not be possible to read it. On some used dvds I bought from Blockbuster, I had to polish out the scratches somewhat before I could rip them to the hard drive and make a good copy.
Don't know where you are located, but here in the US, I use a product called Showcar Glaze #7, made by a company called Meguiar's. It is normally used to put a high gloss finish on automobiles. Use this polish in an in and out motion to buff out the scratches, not round and round the disk.