Having customers for life is a long, long time. Situations change, and people change. The foundation of a wonderful relationship two years ago may not mean anything today. Your relationship with a long-term customer is similar to a marriage. The relationship must evolve to stay vibrant, alive and satisfying to both of you.
So never stop selling them. Every time your company comes out with a new product or service, pitch it out to your current customers first. If it's really a new and improved model, don't you owe it to them? If there's a limited supply, shouldn't your best customers get first shot at it? Always add value to their current purchases.
Excerpted from Creative Selling: Boost your B2B sales