Why should employees act as if customers are their employers?

Because customers are the source of income to the business and employees work for business

Explanation:

Let us understand the concept of business and source of income. We say "Customers are king". Why is that so? We get income only from customer. Employee gets income from employer. So, how employer gets money? It is from the customer. So indirectly customers are the employers who act as the source of income. So if business is running fine then only customer will be available. If customers are available then income is available.