There's an expectation from the market that all nonfiction authors are subject-matter experts. In fact, you'll be granted this status the minute your book is published. However, youu2019ll also be expected to demonstrate your expertise. Unless you can show clear evidence of your results, your readers will dismiss your findings as unsubstantiated. In preparation for writing your book, you'll need to accumulate a significant number of testimonials from clients that you can then weave into your text as case studies, anecdotes and stories. Not only will your audience need to see your social proof so you'll be considered a credible expert, but also you want them to identify with your clients.