I think it would be a good.. great idea if people could close their own threads, it would save mod's time and help cut spam.
If someone wants an answer to a simple question and it is answered in the 1st reply there's no reason for the thread to be alive any more, for example:
http://forums.d2jsp.org/index.php?showtopic=29924915&f=115

he instantly got his answer yet other people find the need to repeat what was already stated (myself included shamefully) and make this topic bump up just because they can boost the post count, because if they honestly wanted to help they wouldn't reply so that topic would be off the 1st page, removing clutter, and out of our lives.

Yes, it has been suggested before and denied for a simple reason: people would abuse it.

no, already a suggestion in rotation.

was one last week and the week before that.

denied everytime. not a good idea.

This indeed could be nice, people would abuse it, though..

In trade section = maybe, but would still be to much.

Overall = no.

not going to happen