Taken from
Trade-in allowances at 55k for 2000W 306 DTurbo 2.0HDi 3 door. Excellent condition £5,128 Average condition £4,547 Below average condition £3,926
The AA website used to advertise that they used Glass Guide - not on the website now.
Parkers always overvalue.
If the garage are using CAP (Car Auction Price) the value will be even lower. Some garages take an average between Glass and CAP.
A main dealer may not want to retail a car with 55,000 covered. If they are trading it on they will be relying on their buyer to steer them on the value.