I'm in the fundraising business, but the answers are basically similar. Saying how much you value the customer--not just her business but her friendship. That means you have established a friendship by asking about family, work, favorite sports team, etc. Calling by first name, if appropriate, and making certain that sales people are fully trained in expectional customer service.  Customers expect good service, so give them excellent, above expectations, service.  Than follow up the sale a day later with a call asking how everything worked out.