When you ask a customer for a referral, much like asking someone on a date or applying for a job, you become vulnerable to an uncomfortable possibility: rejection. And even worse, if a customer doesn't like your company enough to give you a referral, it's possible that you've alienated them by asking for one.
The solution: Only ask for referrals from loyal customers. But how do you know for sure whether or not a customer is happy with you and your service?
Issue a survey as part of the post-sale process. Consider surveying the customer about a week after purchase, when feelings about your company--positive or negative--are still vivid. Free survey tools like SurveyMonkey and Google Surveys make it easy to do so.
While any survey will help you understand your customers' sentiments, a question like this is valuable for referrals: "How likely is it that you would recommend [your company] to a friend or colleague?" By asking customers who already like your small business, you'll increase your success rate tremendously.