If you sell to consumers, and you have a large list of existing customers, one of the most effective ways to find more is to build a customer model. Send your list to one of the modeling companies, and they match the people on your list to their database. Where your list overlaps theirs, they can pull all kinds of information about your customers — their buying habits, hobbies and so on. Then, they can provide you with a list of people in your market who have those same habits, likes and dislikes, so you’re marketing to people who already look a lot like your present customers. A smaller, tighter prospect list is always better.