Only charter members can sell, if you wish to sell you need to become a charter member, cost $20 a year. Link at top that says charter member leads to signing up.
I've bought and sold there numerous times, not a problem one.
I make it a practice to go look every couple of days. I got real lucky one time lurking in the Active Topics forum, saw something I really wanted just posted a moment ago. So I jumped in there and said "I Do". Less than 3 minutes total had passed! Most of the CTX guys wanted it too! I got ribbed a little