In fairness, they are offering to buy ANY car regardless of condition. They need to be sure that they can sell on ANY car they buy at a profit, even the worst cars, so without a full inspection they are going to have to assume the minimum value for every car.
It doesn't take a genius to work out that if you've got a mint car, you never going to get a good offer of these people, but if your car isn't even fit for the scrapper and you haven't got a cat in hells chance of selling it privately, then they may actually be a good option. Don't forget, you have to pay to scrap your car these days!