I don't think he will agree to receive less if some customers cancel. Keeping the customers happy is your responsibility, and its in your control--only you have your books and internal records.
Be sure to send out a good letter to your new customers (hopefully) assuring them that you will take good care of them. Promising top-quality service. Pointing out the advantages of service from your company. Explaining how you use better equipment, and better products. Explaining how your people are well-trained and highly skilled. Offering to solve any complaints by yourself meeting personally with them.