Sign up for Amazon's affiliate program and use your own affiliate links on your links to amazon.
-------
Also, as commented below - I posted the first of these recurring income threads almost two years ago - I'm now compiling some stats, data and insights [1] for myself so that I can learn how to boost my numbers closer to yours :)
That's actually a good call. I'm already an affiliate from another blog I have. I've been meaning to change those links and I hadn't gotten around to it. Thanks for the reminder.
The book is actually a tiny portion of those sales. I'm one of those rare guys that makes money off the thing the book is about and not that much teaching people about it. It does make some though so I include it in the calculations.
Mostly I haven't done much marketing for it outside of my blog so far. I've been toying with some other ideas for it, but I haven't really had the time to devote to it. Mostly it's just a side project I've had fun with.
Derek I've used your Debt Snowball app and it's been immensely helpful in getting my financial house in order. I've signed up for your newsletter and will be checking out the sample chapter of your book so you may help even more!
http://buildanappbusiness.com/
https://itunes.apple.com/us/artist/30-south-llc/id331245760