I don’t make much money on eBooks (compared to writing ten books for publishers like McGraw-Hill, J. Riley, Springer Verlag, etc.) but I so much prefer self published eBooks - so easy to push updates and new editions! I have one eBook that sells very few copies (on the super niche Lisp Hy language) and I decided to make the minimum price free last month. The sales actually increased.

Anyway, probably the best model at least for me is to make eBooks freely available, but with an optional ability to pay for a book.

I'm currently trying, and failing, at the paid only ebook option. Maybe I'll give this a go. What is your book?

My marketing strategy is basically give away ebooks for free at launch and promote on social media. A few readers still pay for them (which is what I wanted from donation model). I write short books (about 100 pages), so I end up doing 2-4 a year (but losing interest now). Then bundle related books. And so on. You can find book links from my profile.