Something I wrote recently on this

https://news.ycombinator.com/item?id=9207290

"It used to be common to see "paid advertisement" inserts in major magazines. Sometimes going on for a dozen pages. It was clear they were PR pieces: typeset differently and with a different editorial style than the rest of the magazine. Sometime in the mid-2000s they simply seemed to go away and now the magazine just uses the PR pieces as content filler, completely indistinguishable from the rest of the periodical."