Asking for referrals is a great way to find new customers. But being more referable will work even better according to John Jantsch in his article 7 Signs Your Marketing May Need to Evolve. Once you've got people talking about you stop paying for expensive, ineffective advertising and rely on referrals only marketing!
You need to become so remarkable customers can't stop talking about you. Seth Godin says "when you amaze and delight, people talk about you". Godin goes on to state that if your mission is to always make it right and over-deliver on everything, you have discovered the most important secret of marketing. Find out what your customers don't like and fix it. How? Use customer reviews and feedback combined with a specialized auto repair website. Then find out what your customers like and do more of it. And then provide service that will amaze and delight them. Get them talking!
Sure, keep asking your customers for referrals, but more importantly, ask them to talk about you. The massive popularity of social networking, such as Facebook, Yelp, Twitter, n49.ca, etc., is a powerful form of customer driven marketing you must take advantage of.
After you've become remarkable make it easy for people to talk about you. Make sure your business is listed on all the popular social networking websites. Encourage your customers to make comments about your business. And then monitor and reply to those talking about you.
Set up a repair shop website with an Invite-a-friend or Recommend Us system and encourage your customers to use it. If your remarkable enough all you need to do is tell your customers where and how they can recommend you.
As Steve Martin said, "Be so good they can't ignore you".