Kristian Köhntopp is a user on octodon.social. You can follow them or interact with them if you have an account anywhere in the fediverse. If you don't, you can sign up here.

Did Google ever sanction itself for violating advertising or SEO guidelines?

I seem to recall this happening. Some business unit of Google violated an aspect of SEO guidelines. Google penalised that unit by reducing its SERP ranking / weighting.

Does this ring a bell for anyone? ~2011 - 2015 timeframe, possibly.