You can build the profile in DJ-Classifieds with the custom fields: https://dj-extensions.com/faq/dj-classifieds-faq/how-to-add-custom-fields-to-user-profile-in-dj-classifieds but I suppose this is something you already know.
Here’s an example with a profile with custom fields: https://templates.joomla-monster.com/joomla30/jm-myoffers-v2/en/about/classifieds/classifieds-user-profile-1/emilia-clarke,867
But I guess you mean something different? Displaying those custom fields details in the advert’s details page? https://templates.joomla-monster.com/joomla30/jm-myoffers-v2/en/about/classifieds/category-blog-layout/ad/beauty-health,76/colorado,7l/beauty-wax-candle,180 so there would be the custom fields also visible in the “Created by” section?
7 votesVersailles commented
If we can have the user name or avatar in smart table view linked to all his adverts under expiration date and Views that will be helpful also if we can show the user filed group (business or private)