No advertising is better than a customer saying they like your product. You may have all the answers and enthusiasm, but you have a vested interest. People connect with other people so having a real life human endorse your product on their own is gold. Make sure you put testimonies:

• On your flyers
• On your website
• On your bookcover
• Everywhere you can

If you can't find anyone to give you a testimonial then your product probably sucks and you have bigger issues than advertising.

Do you get testimonials? How could you integrate testimonials into your marketing?