As above, use your insurance, Even if its being repaired at a mercedes main dealer!
I had a neighbour hit my bumper on my last E63, clear cut case, she admitted it was her fault (I wasn't even in the car!) took it to the official Mercedes bodyshop (Lancaster group) who said they can look after the whole claim for me with the other persons insurance company and lend me an equivalent car. As it was the main dealer official bodyshop I didn't think too much of it, they lent me a Porsche Panamera as a courtesy car which was nice (but not as nice as my E63). It was handled by an external claims company.
repair was done, Porsche handed back, all good? no... the bill for the repair was about £2.5K , that was shocking alone as all it needed was repainting really. on top of that £8k for the hire of the Panamera! The other persons insurance company was happy to pay the repair bill but disputed the hire car charge. The claims company then get a legal solicitor involved who is acting on my behalf , so basically if they loose the case I would not only be liable for the £8k hire charge but also the legal bills! So an easy repair was not getting extremely stressful.
We ended up having to go to court where the judge basically told the insurance company it was her clients fault, it was an equivalent car lent for the inconvienience and they should pay up. This was all over a 6 month period. so be wary the stress of potentially having to pay up out of your own pocket.