Dealers will always give bottom dollar for cars, there view is they need to make at least 20% and if there is something that needs fixing that could take another 20%.
There is a shortage a good quality used cars at the moment, if you need to sell it quickly by all means go to a dealer but online auction sites will give you a better indication of what a car is worth if they sell.
Tonight I went to the local car auction with a friend who needed a car quickly, we picked up a lovely one owner from new 03 reg Astra with 55k, £1025. The previous 03 Astra had double the mileage and only achieved £600.
At the same auction a few weeks ago an 2005 Aero 9-5 Estate with 98k achieved £1400, it needed some minor dents sorted but what a bargain. If I had the spare cash I would have bid but then it would not have been so cheap.
At the end of the day a car will only get what somebody is willing to pay for it. At the moment Saab is not good news in used cars but that means there are bargains to be had if you want a good late car or a low mileage early car.
Steve