They're there to make a profit, as much as possible.
TV advertising ain't cheap and they've got to pay to move the car from wherever they buy it to wherever they sell it. Auction at a guess, nearest to the seller.
Their only income is the difference between what they pay you and what they can flog it for.
I wouldn't be surprised if they're the same companies that buy your gold, and they've been 'outed' in recent radio and TV programs as paying as little as 10% of what you can get from a high street jeweller.
Sold deceased f-i-l car through them a year or so back. The price was lower when I got there, primarily because of the amount of filler and respray which they showed me (and which the old boy hadn't told us about!). It was a very easy transaction and suited our needs but wouldn't be right for all.
... because we are really lazy and haven't written that bit since we launched this site on Monday. ;-)
Keep the suggestions coming though and someone here might get around to prioritising and adding!