Chuck added this for me as a paid custom feature 2 years ago and it worked great. After a few upgrades though I could no longer integrate the custom work and let it go.
It worked perfect. All registered users could have, say 20 ads. If they wanted to post another one then they neeeded to delete an old ad to make room. Kept the playing field level.
Now, my ads are messy as guys routinely try to abuse our classified limits so all I can do is let them post a max of 20, then that's it, they are done. Of course a user would sign up new names to post more ads so I do not use that feature and spend a fair bit of time to review the ads and anyone with more than the limit gets an email and a trim job, very tedious.
I'd love the other system again. Very smooth and fair to everyone.
Thanks for listening.