Always ask a satisfied customer for referrals! Ask for the names of people who might also like to buy from you. Get addresses and phone numbers and follow-through with a call or card.
While this is a common practice among large ticket sales, it can also be used in hundreds of other situations. Suppose you call people to introduce yourself and invite them to come to your business. Most people will be surprised and pleased by a personal invitation like that. And it beats sitting around hoping someone will come in.
Of course, the more information you can get about a referred person the better. But don’t make giving referrals a big job for your customer. A name and address or phone number are all you need. You can look up other data if necessary.