At this stage that would be a custom job, as it would not be possible with any of the available options, if your problem is with spam, then maybe look at alternate options to deal with the spam.
This would include allowing a few free posts in a membership plan then charging for additional posts, to un check any automated posting or edits so that you approve of any new listing, the same as gum tree and others, ban users who spam, add and allow posting in other categories to be fairer to people and the list goes on.