If you don't want to upgrade to new Osclass 3.9.0, you can use use this guide to remove Osclass Market from your current installation.
This guide covers most, if not all, changes required to un-tie your site from Osclass Market
If you know some changes that we forgot, post it on our forums or contact us via the links above.
As a test if this mods were successful, we put
We visited admin homepage, plugins, themes and language pages, settings page, we checked for updates, we ran cron, etc.
There wasn't a single cURL log that says that a request has been made to Osclass.
Also, all this changes were made on a live site as the guide was written. There were no problems, errors and warnings.