There’s no other way to say it: testimonials rock! It takes the pressure off of you bragging about how awesome you are and let's other people build your authority for you.Testimonials prove that you have worked professionally and is a psychological trick to clients that says "well if THAT person said that about you then you must be good".
Who hasn't bought something completely useless off of Amazon because the reviews said it was "amazing!"? Here's a script asking for a killer testimonial from past clients.
Remember, you need to craft a testimonial to THEM FIRST and make it from the heart. Think of giving them a lovely gift (your testimonial to them)and not wanting anything in return. If they do send you back a testimonial then woohoo!
Best of luck.