I have tried many suggested methods to remove scratches on a glass tank and failed every time. There are those who assure me it works but it does not for me. I have used several different powders and compounds as well as power equipment and all have failed. I have been able to scratch the surface using things like steel wool but I have never improved the situation. I can make a larger scratched area but never smaller.
The problem with having it done by pro glass shops is that it costs more than buying a new tank!
Acrylic scratches would seem to come out easier but I have no experience with that.