Can't you just have a separate forum? If people want to participate, they can. Caveat emptor and all.
I'm not saying make it big feature. Just a little section for people who want to deal with their internet buddies.
Require like 100 likes before you can list anything or something. I am not saying facilitate it. I just don't see the need to bar people from offering tickets. If you don't want to participate, you can avoid it.
My preference is for open play within boundaries. I don't care much for heavy handed moderation on the web or elsewhere. Folks can make their own choices and live with the consequences.
Eta: I've been a part of many forums where people exchanged or sold tickets, sometimes they made a profit. More often it was a loss. The nature of our stadium and team means no one is going to make a killing reselling our tix. On other forums I've been a part of, it hasn't been an issue. It actually seems to facilitate camaraderie on the board and in real life. But then again, my friends and I dont mind playing poker with each other either. Btw, it's so weird that you make that analogy. Who doesn't like poker with the fellas?