I indicated that entirely avoiding conflict was impossible. It is possible to reduce the chance for it by always setting appropriate expectations, and when given a chance to tell a customer, "No," one should do so. It seems counter-intuitive, but rejecting impossible requests does not damage a relationship with a customer. Rather, it helps set the tone for dealings. That way when you tell a customer, hopefully rarely, "No," they understand it is actually not something you are going to budge on. Trust me, when a customer hears, Let me ask my Boss, or I don't know if we've done that before, etc., you are essentially saying, YES.