I think like other forums I am apart of, JSP should give you the option to close your own thread. Even if specifically for trade forums.

Why would this be handy?

If you post an item and it is sold, nothing worst then having offers flood in after items have been sold.
If you have a question thread, its answered, you can close it. No need for redundant spam and bother staff to close a thread.
OP notices thread is getting out of hand, shut it down.

Among other uses, I dont see how this would be a bad thing and it would help users self maintain the forum.

Yes/No? Why?

voted no

No.

Yes, but with a limit on how many topics can be closed in x amount of time.

Earning rights like this one (many examples of things that are good if not abused) would be cool; but I don't see it happening.

This has been posted more times than I care to count. And rejected as many times.