Complaints can be your best friend in sales. Just because a customer voices no gripes over an extended period, it's not safe to assume that customer is satisfied. If properly handled, complaints can be customer-saving opportunities. When a customer voices a complaint, it gives you a chance to get to the root of the dissatisfaction and hopefully remedy it. There are two kinds of unhappy customers: those who gripe and those who are closed-mouthed and simply jump ship. Be grateful for your gripers.