It may be a matter of experience and perspective. I only discovered AWS about 9 months ago or so and Amazon Affiliate program two months ago. I figured how to do elastic servers by hacking around, but the other services are still beyond me, especially which ones I need and how to connect them to each other. I've read lots of stack exchange posts on how to do various subtasks like installing an SVN server, but I wouldn't mind paying to read a coherent presentation introducing the most relevant AWS services for my needs.
If you know of a thorough introduction to the use, caveats and good practices on AWS through stackexchange, please let this author know. So far I have only found thousands of Q & A, which is like eating ice cream with tweezers.
As far as OP goes, try to find folks like me who are starting small/home office businesses in niche markets and make your book part of a larger bundle of educational material on things like mailchimp, Quickbooks, etc. Also, typical marketing for products like this is to give away the first chapter for free.
Also, find blogs of people whose readers could use your ebook and write them each a personalized email saying quite simply, "I made this book. I think your readers might like it" and let them decide if they feel like writing about it. You'd be surprised how many influential people you can reach in 4-12 hours of searching for blogs and writing. Good luck! Also,
I see you link to menutail in your Profile. Get a link to your gumroad up there, pronto! Get it in your sig and in your email, too.
Also, start a blog in which you handle a new topic from the book in introductory depth each week. Venkatesh Rao did a good job promoting _Tempo_ this way and it can add value to the original material long after the publishing.