“It’s word of mouth– amplified”.
Ask your clients to post a review online. Two great places to start are Yelp and Zillow.
Both sites will require your client to have an account, but it only takes a few minutes.
Clients can review your profile on Zillow by going to http://www.zillow.com/directory/real-estate-agents, searching for your name and clicking on Review.
For Yelp, they can go to the homepage http://www.yelp.com and enter your name in the search field.
Of course, if you don’t have an account your clients won’t be able to find you.