I sold my 159 to TheCarBuyingService, at their Coventry office (which is actually just a bloke with a laptop in a serviced office). Got a whisker shy of £7k for it which wasn't a million miles away from the £7.5k I was looking for as a private sale. Obviously it was less money than I might have got, but it was an easy and rapid process, and they were pleasant guys to deal with.
It was slightly curious though at inspection and handover - as a private buyer, I'm mostly interested in the mechanical condition, any rust, whether the various bits of equipment work, etc. Their guy gave the car a cursory glance under the bonnet, and drove it back and forwards literally 3 meters in the car park and that was it mechanically/electrically. However he was extremely thorough with regard to dents and scrapes, to the point of using a special widget to measure paint thickness all over to spot accident repairs!
The car was actually fine - but it could have had all sorts of issues, and he would have had no idea until he went to drive it off to wherever their storage compound is.
They did knock a bit off for various things (as expected) but I still got hundreds more than WBAC were offering as their initial valuation, let alone before their knock-downs. Overall, I'd recommend them, unless you're in no hurry at all for the right buyer to come along and pay (a bit) more.