How do we value our cars?

So over the weekend I had an accident and now I am concerned with valuing the car. I have antique insurance and told the insurance company my 65 Barracuda /6 (Hopped up) was worth 18-20k. I got that number from the Haggerty valuation tool. Nada values my car with a slant at 16k.

As the title states how do we value what our cars are worth?