And by the way, the only other 2 paths you can take as a company to evaluate something like AWS are 1) trusting AWS tech sales; 2) trusting xyz consultant. On point 1 you clearly have a bias and even without the bias you could be talking to a company selling a technology that is a bad fit for you (like all those trying to do BI with a Cloudera stack). On point 2 you can find consultants expert in AWS or xyz tech stack, but it's harder to find professionals that know the technology of the present day AND also can make good guesses at where tech is going to be 5 years from now. On top of all consultants are paid to be confident and that's exactly what you should avoid, you should be selecting technology knowing that things might change.
That said the $25k in quick sales for a technical book is a great result, congrats DVassallo!
A more interesting question is what the sales level will be once the dust settles.