How to define your market when you can't afford to sell every customer

Working with startups and talking about markets all the time means you need a decent definition for what is a market. Increasingly, I like the idea of defining a market so that the business can build its effort towards NOT selling each and every customer, or in-other- words build its effort towards the customers themselves be the sales channel through reference or word-of-mouth. Geoffrey Moore's market definition looks to serve this idea well. He defines a market (originally for hightech) as:

• a set of actual or potential customers
• for a given set of products or services
• who have a common set of needs or wants, and
• who reference each other when making a purchase decision.