This has been discussed, I'd rather it not be removed, as it gives people an idea what something sold for, or if there were problems with a seller, etc.
It would be nice if we were allowed to change the title to add "sold" though.
I'm not sure about this forum, but usually changing the title of the thread requires high level moderator involvement (Woody). A much easier thing to do is have the seller edit post#1 of the thread. Next to the asking price, in large red letters add "Sale Pending", then change to "Sold". This also makes it easy to tell what is still available when multiple items are listed. This etiquette is used on other forums that I sometimes participate on. Saves you from getting your hopes up about that must-have item that you find out is sold on page 7 of the thread. Also allows future sellers to still search and find out what an item may be worth.