A testimonial is basically a positive review of your business, service or product that is told by someone else. And you should know why testimonials are why books are important and should be a part of every business.
Your book gives you a good reason to contact people who are influential in your business and also allows you to stay in contact with your clients and customers. Why is this important? Well if you’re contacting other people in your industry that is related to what you are writing you are basically borrowing the trust that they have built and adding it to your own and with clients and customers you are allowing them to not only sell you to others but allowing them to keep on selling you in their own mind. They have to justify why they decided to go with you and they now build up more concrete evidence of it simply by writing down what they think of you and your business.
Now these testimonials can be used in your books but they can also serve other purposes with promotional materials, they can be used to sell more information on your website and any other promotional material you might come up with.
So now that you have this social proof you don’t have to justify the prices nearly as much as you did before because other people are already doing it for you and you can also feel good about what you are selling because people are telling you point blank how it is affected them and their business in a positive way.