One of the odd things about some business organizations is that they spend so much money to lure new customers and spend so little to keep them after they've been landed. It just doesn't make sense. Taking customers for granted is routine in some larger organizations, where mere bigness generates an attitude of indifference. Loyal customers are an organization's only protection against bankruptcy, and losing them because of neglect or indifference is downright sinful. Not only do satisfied customers continue to fatten the till, they often encourage others to buy. This is advertising that doesn't cost a penny. And although there are always problems in giving good service to customers, maintaining their patronage(光顾) isn't all that difficult. It's a matter of attitude, of believing that everyone who buys from you is entitled to the best treatment you can deliver. Plus giving just a little more than you have to. We said there are always problems in giving good service to customers. The reason, of course, is that no organization is perfect, and there's many a slip: unreasonable delays in filling orders, shipping the wrong merchandise, failing to answer letters promptly, and so on. Sometimes these errors or failures can't be helped. For example, if you can't get parts because of material shortages or a transportation strike, customers may be denied the goods they've ordered. And not infrequently the customer is to blame—for example, failing to clearly identify the article or service required. Yet no matter who is at fault, customers whom you value highly should generally be given the benefit of the doubt. Note that we said 'customers whom you value highly.' The old saying(格言) goes that all customers should be treated alike is a myth. Customers who repeatedly place large orders and pay for them will naturally, get more attention than those who buy infrequently and have to be badgered to pay what they owe. However, you have to make the assumption that all customers are good unless proved otherwise. The main idea of the passage is best expressed by which of the following? _____