I used to always sell my cars privately, as they were always very well looked after they sold very quickly. Over the past ten years, or so, I have noticed it is becoming more difficult to sell privately, too many tyre kickers looking to screw you. Also dealers are now keen to take your car in part-exchange, and are willing to give you a very good price, also you can negotiate a discount on the new car before discussing the part-ex. This was something a dealer would never do in the past, if trading in a car they would almost always charge you full list price. WBAC, and the others are merely middle men who buy the car and pass it on to main dealers. Lots of the main dealers are now actively seeking to buy used cars also.
The internet age has made it much easier for us, the consumer, to get a much better deal on cars. When I think what I paid for a new car 20 odd years ago, it is not much different to the cost now. Paid over 8K for a Pug 205 in 1986 (from a broker 400 miles away from home), paid 10K for our new 108 TOP from a local dealer who beat the best internet price I could get. He also matched WBAC offer for our Fiat 500 trade-in.