Everyone knows that it's less expensive to service an existing customer than to get a new one. The exact figures vary with different businesses but if you try to quantify how much in advertising, entering new data and unsuccessful attempts each new customer costs your business, you might be surprised. Yet existing customers leave businesses every day and most businesses do little to keep them.
If you make an easy sale and the product performs as expected, that's a customer you probably won't lose but one who hasn't developed any great loyalty to your company either. It is the customers who, for whatever reason, experience problems with your product that represent a teriffic marketing opportunity. Customers realize that there can be problems with any purchase - it is what happens afterwards that is important.
Customers leave because they have had problems and the problems have not been properly addressed. Customers develop loyalty if they have problems and the problems are addressed in a positive way and are solved promptly.
The reason that many companies lose customers is that traditional ways of addressing customer problems have not been satisfactory from the customers' point of view. A page on the Netscape Business Center site has some answers to this problem. By using the Internet to deliver customer support, you can make solutions available at low cost and in a customer-friendly way.