I experienced what you are encountering right now.
Just to find out what's wrong with my C280 they told me that the computer is spitting out different info. so they need to replaced the wiring harness w/c cost me $685 + $590 labor.
Later found out that one of my ignition coil is bad w/c cost $130. You what the dealer told me?
They did'nt charge me to install my new ignition coil. Sounded like I still owe them one after I paid them $1400!! Not even a car wash and initially they won't look at it at all. They wanted me to wait for 3 weeks for an appointment.
Customer service as they call it...