When silverplate arrives tarnished and discolored it is a leap of faith to hope that it will polish up nicely. Usually dark to black tarnish is a good sign that there is still silver plating, but that isn't a guarantee.
Pits and scratches can not be removed. The plating is not thick enough for an aggressive polish. A light a skillful touch in polishing silverplate produces the best results.
Silverplate Tray Polished
This tray arrived very dark with tarnish. (Look for the before photo in this gallery of images.) Despite the oxidation, the tray itself was in good condition.
I am always willing to polish your silverplate, but there is no guarantee regarding the final result. If the plating is worn off there is nothing I can do, however enjoying silver that is not perfect can have a lot of character.