There are two sides to this problem….one yourself in not wanting a damaged new car and two….Motability not to concerned as long as you sign for it and accept it and in 3 years time they can sell it at auction and make a profit .
At the end of the day if you are not happy with the repair then don’t sign for it …then it’s down to them to sort out a replacement , they will be hoping you are desperate to get you new car so you are mobile again and may push you into signing saying the old car has to go back if you have one .
As others have said it’s more common than you think getting anew car bodywork repairs , as long as the colour match is good then except it but also check it shuts correctly and the electric window works as does the central locking .
Good luck .