I think you should be able to exclude comments and close the thread once Sean sets that up.

We decided against allowing edits to the original post beyond the usual edit window, because that could defeat the purpose of the archiving system, which will retain ads after thirty days for research purposes and in case of disputes.

So if you want to update and indicate which items have sold or which items are still available, you could mention that as a comment to the thread or occasionally post a new list within the thread, or if it becomes a real mess, just close the thread and relist.