The most convincing thing you can tell a prospective customer is what another customer said about you.
So ask for feedback from your customers. New customers see far more credibility in what a customer has to say about a product than the traditional manufacturer's blurb.
Every customer interaction is an opportunity for feedback. So ask for feedback and publish it on your web site.
This has two positive effects:
Prospective customers see what others have to say and this builds credibility for your business.
Clients love to be made to feel included, they always have an opinion and most are more than willing to share it.
On completion of every project we send a survey, and publish feedback.
Could your business benefit from a simple process for collecting feedback and testimonials
PS. Negative feedback is even better than positive feedback. By fixing what your customers think is wrong you create happy customers who do the selling for you!