I have noticed on rare occasions that something that was posted long ago, and you think: Surely that is done with. Then you see the thread surface when somebody finds it and asks about it on a long shot; and it in fact is still available (and stop calling me Shirley).
I have looked at older for sale threads on occasion to see what one might expect to pay for something. It would be nice if everyone would update the subject with a big fat SOLD.
managing the for sale area in such a way would be entirely too much of a headache. if something is sold, then the seller just needs to state that in the thread.