I thought Craigslist had ads in addition to user-submitted postings, which is I wrote my comment the way I did.

Apparently Craigslist doesn't actually have "ads" in the usual sense: https://www.quora.com/How-does-Craigslist-make-money-if-it-d...

It seems the difficulty here is identifying what is considered an advertisement, beyond the obvious display ads which are not intrinsically a part of the content that they are embedded in. But fortunately display ads (and their brethren) are the most problematic, so I think we would get significant mileage just focusing on that.