Reading this makes me happy as I'm currently working on a service [0] (not available yet) to allow sites to do this. The goal is to facilitate and make ad selling/scheduling easy while having websites/etc. serve the ads themselves, ensuring no tracking (by my service) is possible.

A lot of people are already doing direct sales via mail and then work out a way to get paid somehow, which can be cumbersome. Hoping to make that easier, while also improving the bad, intrusive behaviour around ads.

[0] https://www.adsfromsource.com