Actually, I did this long time ago. Back when we had flee markets around. Silver springs and Harrisburg Drive in flee markets. I would set up two EM pins on free play and sell what ever other stuff I had. Put business cards on them stating I buy and sell used arcade games. Mostly it was just people wanting to play or look at the games. Once in a while I would get someone tell me how they had an old game sitting in their basement and wanted me to come look at it. I think I only sold 1 or 2 games from people I met there but what the heck.
Not much difference from putting wanted ads in the paper. You do end up getting to chat a lot about your hobby though.