[mkdltn]

First a disclaimer, I have never removed pencil marks from a card but I am an artist ( stayed at a Holiday in to!) and my two choices if i were to try would be a grey kneaded eraser that picks up pencil just by applying pressure without the back and forth that could damage the card or an eraser that is white called Magic Rub it has excellent pick while at the same time not so abbrasive.

Update. did a little experimenting and the gray eraser is a bit aggressive.