Reviews and testimonials are huge when it comes to selling yourself online. People you have never met are looking to have a "good" car buying experience and reviews are the only thing they have to go on until they meet you in person.
Make it a habit to ask for a review from every customer. Fine tune the way you ask until it becomes second nature. As you get more reviews, they will be sent to your Facebook page and hopefully your clients will share them on their Social Networks as well.
Continually over deliver and you will see your reviews and sales soar to new heights.