That's only the initial quote mind, they assess the car in person after that, and will pick on any faults to drastically reduce the value. Don't hold your breath for much more than half of the original quote 
Not my experience. Sold a hot hatch to them, my car was perfect, they appraised it and agreed & not a penny reduced on the price and paid in full, plus got my tax back as well. You hear these stories of them knocking the price down but even as I waited 2 chaps came in with so called perfect cars that clearly werent perfect. You could see them get upset at the appraisal but thats because they werent being honest. There were loads of scratches, little dents etc that the owners overlooked but this company didnt. Understandably they are a buisness and need to make money and if your car is not perfect they will have to reduce the price to put things right. And the branch I went to seemed to put absolutely no pressure on these 2 people to sell immediately either. Both of them were told that they had a week to decide during which the offered price would be held and after that would have to reappraised for better or worse. In my eyes you cant get fairer than that.
If you go to them expecting to get top dollar for your car then you will come back feeling let down. Make allowance for a profit for them, any rectifications to your car, weigh it in against the price you get, the lack of hassle and the rapidity of sale and make a decision. In my case I needed the car to be sold as I was getting tired of waiting around for idiots to come and have a
joy test ride in my hot hatch.
Lastly they are not the place to go to to sell low value cars like Omegas and ancient cars.