We once had a 6-year-old Porsche that was totaled (rear-ended). It only had 20K on it, and the insurance company said they were being generous in allowing us high retail price and adding the X-cents per mile for low mileage. I told them that the amount for the low mileage wasn't enough and if they wanted to settle for that amount they could find me one with the same mileage. They said they couldn't find one that year with the same mileage so I said fine, just find me any year with that mileage that's in the same condition.
I was in no hurry as we had other cars to use. They finally settled for a few grand more and I was able to find one 3 years newer with only a few more miles on it but tricked out better.
I think what helped me was that I was persistent but in no hurry to settle. And I had a reasonable argument for wanting more. I was dealing with my own insurance company, as the guy who rear-ended us had no insurance.