Well, casual sales do occur at our forum. Personally, I am most comfortable dealing with the members I know, for instance I initiated purchasing Gene's M2 last week when he mentioned he intended on selling it.
And of course, all formal sales must be posted in our classified section.
I think it is always best for both parties involved to deal in good faith, of course, but also within their acceptable level of risk. That is important when dealing here, ebay or anywhere else on the internet.