I definitely have a following, as does my co-author but most of the sales came from giving away (or publishing) chapters and linking back. To this day our number one driver of sales is people who have read our blog posts about how to get press or how to do SEO, because it's actually actionable stuff.

I can attest to this strategy working, albeit on a much smaller scale with my presale right now. Smaller price point, assuming much less traffic on the medium posts.

Hell, I have more revenue in presales in a little over 6 weeks than 18 months of trying to build SaaS apps.

So you contacted marketing oriented sites and offered them free chapters to publish in exchange for the book publicity?

I suppose that's often what you see in newspapers when you read a short excerpt or short story based on a book, must be reasonably effective?

Nah, I just posted on Reddit and Medium as blog posts, that kind of thing. Honestly I have an entire 196-page book of marketing strategies I actively use, so... you know.