Please the customer first!  The customer is your boss, your employer!  Keeping them happy keeps you employed.  Caution!  In rare cases, there are times to fire a customer for being unreasonable, demanding much more time than average.  If you find yourself in that situation, one needs to let the customer go and move on.  Remember, you are not going to please everyone or have a workable situation with everyone.  The key is to recognize it and deal accordingly.  The customer is "always right unless they are wrong!"  Good hunting!