I like the idea of closing after 30 days inactive. But, could they still be marked 'sold' later? I think a lot of guys have gotten better at marking them, so if they can't go back the thread will always look like the item is still available. Effectively making more 'open' threads, just not on the front page. Same with people opening a new thread instead of bumping it. The original thread is still there and looks like it never sold.