With DJ-Classifieds Importer component, it is easy to import ads to DJ-Classifieds from the external feeds. We have just released the updated version that brings two new parameters suggested by users.
In user_id you can just provide the ID of the existing Joomla user.
With user_email system will find the user's ID by comparing the email from the database.
If those fields are empty or missing system will use the default user from feed configuration.