I would assume that his blog posts are what convinced quite a few people to actually buy the book. That said, I'm not too familiar with the book sales industry.

I am familiar with consulting. Initially I thought that giving all special knowledge away for free would be the worst thing I could possibly do.

Boy was I wrong.

Nowadays I give presentations detailing step by step exactly what people need to do in order to achieve some outcome, with as goal that they could do it 100% by themselves if they want to.

My theory is that this leads to more sales due to me becoming more visible + it builds large amounts of trust + the best possible clients are going to be very busy + the best possible clients are aware that they could implement all my advice by themselves, but if having me on board as well increases odds of success by as little as 10% (or increases the total impact by as little as 10%), it is still going to be a win to have me on board as well.

I have the entire text of my first book available online for free. My sales have been way more than I ever expected, year after year.

It accomplishes a few things:

* While I was writing the book, I published each chapter online as I finished it. The top of each page has a link to my mailing list. This was a great way to build an audience. By the time the book was complete, I had a mailing list with thousands of people I could tell about it.

* It lets readers try before they buy, which builds confidence.

* It makes for a very effective web presence. People searching for the topic are likely to find it.

* People really love it. Even if they never buy it, they become fans because they've been given something for free. That in turn makes them walking advertisers for the book. I've had people who read the entire book online buy a copy afterwards just to say thanks.

* It enables people who can't afford it to still have access to the material. This may not make me more money, but it's important to me.

No, that's not an issue at all. I have hundreds of articles on my blog that are also covered in the book:

https://vladmihalcea.com/tutorials/hibernate/

But reading the book is easier than browsing the articles because the book has a certain structure while the articles focus on a single topic only.

Packaging, convenience, lack of redundancy and logical structure are worth a lot if your time is valuable. ConversionXL sell video courses for $600 each that have ~the same content as their endless series of blog posts. But the video course has a beginning, middle and end. It’s a polished finished product. The blog posts are raw material. Plenty of academics do similar things when writing books. There’s vanishingly little in any of Bryan Caplan’s that didn’t appear on his blog first but the books are far superior at conveying a theory, rather than more or less disconnected facts.

Many in this space have made good revenue by literally just packaging blog posts together with a nice cover and no additional editing. Maybe a small intro for each group of related posts.

If folks really like your content, they'll often pay for the book just to support you.