I came across a great book - "The Referral of a Lifetime" by Tim Templeton. He shares a system for building a business on continuing relationships with customers and "center of influence" referral sources, and referred customers. A good portion of the book refers to using cards and gifts to build and maintain these relationships.
Every good salesperson knows the two best customers to work with are a customer who is happy with a previous purchase from you and a referred customer. If you work with these people properly, you will have overcome the huge hurdles of winning the customers trust and have at least the seeds of relationships. If you offer valuable products and services to people who like and trust you, the sale is vastly easier than making sales to cold leads.
The book is the story of Susie McCumber, a salesperson who is ready to quit from frustration with cold calling. Susie's friend, Chuck Krebbs, who owns the California Coffee Cafe and Bistro, introduces Susie to David Highground. David Highground becomes Susie's mentor in learning how to build a referral-based business. Other former students of David’s spend time with Susie showing her how they have adapted the system to their individual personalities and use the system to build successful businesses.
The system is built around the Golden Rule - doing good turns for others and building relationships.
You build a database of people that you know or meet. Rank them ABC, according to how enthusiastic they are about you, especially how much they refer clients or customers. Provide excellent service and become known as a reliable, friendly person. Keep in touch consistently, personally and systematically. Express appreciation to your customers and contacts regularly through cards and gifts.
By building relationships and doing good turns for others, you earn the "hall pass" to ask for referrals.