I am pretty sure the default sort order is newest to oldest. (ie most recently posted at the top)
at least it should be.
tom can you provide me with an example?
create date can actually change when the user edits the ad (something we have fixed...but not after 10,000 or so ads were posted)
the order goes from ad number highest to lowest, hover your mouse over the "for sale" or "for rent" box to establish the ad number.