Accident without fault: Estimate only with photos

Hello all, Today my son was cut on his KTM by a can-driver who had to brake heavily to all excess because of the stagnant traffic. My son too, but it was not enough despite the headstand and he hit the bumper of the accident opponent with the front wheel. Luckily nothing happened to him, nor did he fall down. The police clearly identified the can-driver as the cause of the accident. Now the question is how to put the KTM in the workshop for a co-driver. I would be sure to go to the number and not drive the machine until the story has been clarified. What is the usual practice? Or can the workshop draw up a cost estimate using photos?