I know most people on the board already know this, but here is an example of what NOT to do when selling concert tickets to a sold out show.
DON'T offer to sell your tickets to someone, accept their offer to purchase your tickets, attempt to arrange a meeting to exchange money and tickets, and then sell them to someone else, thereby screwing the person who was orginally going to buy the tickets. It makes me people very, very cranky. And it kinda makes you look like a big ole jackass.