Posted By:
Frank WakefieldDESIGN Artgum works well, it is distributed by Sanford.
DESIGN Kneaded Rubber can work well, too. it is softer and will remind you of modeling clay. It is for erasing graphite, charcoal, pastels, and crayon. Sanford distributes it, too.
Neither will get rid of all marks completely. Both can be gently used without damaging most cards. Neither leaves a residue.
And I believe that either could be aggressively used so that a card could be marked by the use. Patience. And be gentle.