It happens, but I sold my old laptop there. The guy was actually from the school I go to now and drove to my house to pay for it in cash. No way to scam you there, hell I drove him to the bank! Just, keep your gun handy
Or just stick with known companies and avoid single public sales.. its the simplest, safest way.... And you dont usually save much money when buying second hand etc as think of the stress etc.......it's never worth it