DV
Jerry Richardson
 You should not have to pay for a diminished value assessment. You should be able to have a reputable car dealer appraise you vehicle in writing. Then tell him your vehicle was involved in a collision and repaired. What is the appraised value with the additional knowledge in writing. Any honest dealership will do this for free in the hope you will return when you buy your next car. If the value is lower, you are entitled to a diminished value claim. DV is a perceived value. The dealers perception is the perceived value. Don't pay a fee to someone when you can do this yourself. Their are companies popping up all over the country trying to take advantage of your situation. If you don't feel confident enough to do this, maybe a friend our relative will go with you to the dealership. We all pay insurance. We are entitled to fair compensation. Don't pay a DV company, it's your money. An honest attorney would only charge a nominal fee for a letter along with your appraisals to get the job done. DV companies are leaches on the system. I own a body shop, my comments are from 39 years of experience.
Car dealers have no validity
Car dealers have no validity when it comes to stating vehicle values because everybody knows they play with the numbers and have a bias in wanting to provide something favorable to a customer in hopes they will come back to buy a car. You said so yourself, "...dealership will do this for free in the hope you will return when you buy your next car." Thus they have a bias, that any opposing attorney would exploit, for fudging the numbers in your favor.
While it is true that some people have collected diminished value with nothing more than a couple of dealer statements, more often than not, claimants are put through the ringer by insurers. It has been my experience that those that have collected in this manner left a lot of money on the table, else the insurers would have never considered it in their best interests to settle.
And, since most diminished value claims wind up court, (at least in depositions) a person has to be careful to secure values from a party capable of passing the test as the unbiased expert whose testimony will stand up in court. You don't want to be in a position where your expert (the person on whom all of your hopes fall) gets dismissed from the case for his bias after years of waiting to get to the courtroom. If this happens, you'll be back to square one (obtaining new values from another expert) and waiting even longer (unless the statute of limitations runs out first).
The same is true of Internet companies that offer diminished value reports without ever inspecting vehicles. These reports carry no weight when the insurer knows that nobody from the reporting company will come to court to atest to the validity of the numbers that have been submitted. They will challenge this and get it thrown out every time, just as they will a dealer's statement of value (unless, of course, it is very low and favorable to settle).
The old saying is usually true, "You get what you pay for."
For some good information on diminished value, check out this slideshow