There is a market place section on the forum, but, in order to gain entry to it, you need to have fulfilled two requirements.
These are, a time requirement, and a post number requirement.
More specifically, you need to have 1) a membership period of six months (180 days), so, you need to have been a member of the forum for a minimum of six months, and 2) you need to have made, or posted at a minimum, a total of 250 posts by then.
I have sold a computer through my local Apple store and was happy to do so; there was still a few months of Applecare on the computer, it was in excellent condition, and it sold very quickly.