Posted By:
leonWelcome to the board. My opinion on pencil marks, and there will be several different ones, is that I have left them. Most of the times they are on the back, in not too conspicuous places, so they don't detract too much. If they are very light you could try one of the "art" erasers that folks have told me about. If the pencil mark made an indention I believe a grading company will ding you for the mark regardless if it is there or not. If you can erase it with no trace of it then you have enhanced the card by 1-2 grades. Good luck on your collecting....and I hope you don't become addicted like some of us 
best regards