A real estate agent may need to show multiple houses to a family of four. Stress benefits to your customers over and over in your letter and in your brochure. Use the power of a third party to re-enforce your message. Chances are they have. We are much more comfortable trying something is we are familiar with someone else who recommends that product.
Many products use a spokesperson to deliver the selling message.
We may not actually know the famous movie star but we often feel that we do. And, if we like the person we may very well buy the product based on the testimonial of the star. In small towns there are stars too. Many small town business people are well known in the community. If you have done work for these folks ask them for a letter of testimonial.