Your profitable customers

Do you know exactly who your profitable customers are? What makes them profitable? Do you know exactly what they buy from you; when; how often and at what price? Do you really know them? Do you always relate to them personally when you communicate with them? Have you ever asked them to buy more from you? Are they buying your competitors goods or services when they could be buying yours? Do you know exactly what percentage of your entire customer base is profitable; does it change; is it something you monitor? What are your thoughts on your unprofitable customers? Food for thought, but worth a nibble nonetheless!