If Repair Bill is out of wack 1978 240D

[SMG78]

Feedback on the fairness of these charges would be greatly appreciated before I dispute them with through the credit card or small claims court.

The car was towed into the shop after it wouldn't start. (the glow plug light didn't go on.) (A mercedes technician tested the battery out before it was towed and he said it was strong. And there was no smoke nor burning before it went to this shop)
The repair shop said that the wiring caught fire (probably shorted out) when the mechanic was working on the car. They took the dash board off and the wiring was a mess. The service station owner implied that the car came in with a wiring mess and it wasn't his mechanic who caused the fire. They had the car for a month.

The bill reads
Replace "cold" plugs $80
(He said it was a bosch and on the internet for the plug and insulator were between $20-30.) Does anyone know how long this repair takes?

Repair electrical wire
Head light switch $89
(There is now a lot of play in the knob and it is necessary to push the knob it for it to turn the switch.)

Wires $100
Lab $231
Total $500.

The outside of the car was filthy. And the plastic lock but on the drivers side was removed and aprox 1/4 inch of the metal was cut off.

Not on the bill --I bought a glow plug relay that he put in. The parts store said it was a ten minute installation.

Also, I plan on bringing the car to another mechanic to check the work out. Does anyone know if another mechanic can determine how the fire and shorts were started?

Thank you in advance.