The brief
The C180 had squealing and squeaking when braking that had turned to grinding, a vibrating, pulsating brake pedal, the stopping distances had stretched, and the brake warning light was on. He brought it in. Those symptoms say the brakes are worn. The squeal and grind mean the pads are down to or past their wear indicator, the pulsing pedal is a rotor that's worn unevenly and no longer running true, the longer stopping is the friction material running out, and the warning light is the system flagging the low pad. Brakes are a wear item, and there's no nursing them past the indicator, so when they get to that point the pads and the rotors go together, because fitting fresh pads onto a worn rotor just beds them into the same uneven surface.
The diagnosis
Wheels off, the front pads were down to the wear indicator and the rotors had a lip around the edge, measured past the minimum thickness, and showed the uneven surface that was causing the pulse. Fitting new pads onto worn rotors doesn't make sense, so it was a set job, front pads and rotors together, to reset the braking properly.
The work
The front callipers came off, the worn rotors were swapped for new genuine Mercedes-spec discs, and a fresh set of pads went in. The slider pins were cleaned and greased so the callipers float freely, everything reassembled to torque, and the brakes bedded in on a controlled road test, a series of measured stops to lay an even layer of pad material onto the new discs. The road test confirmed the squeal, the grind and the pedal pulse were gone, the pedal was firm, and the bite was back.
The outcome
No squeal or grind, no pedal pulse, a firm pedal, full, even bite back at the front, and the brake warning out. The C180 went home with the braking reset to like-new. Brakes are a wear item and there's no nursing them past the indicator, so doing the pads and rotors together gave the car back proper, confident stopping power.