The problem can be the dealer just looks up the book price for a 7-8 year old Golf. These cars are mostly trading above book assuming they are in good condition. If the dealer does not stock this kind of car they will just pay the guide price.
There are quite a few specialists buying these cars from above trade price private sellers and then offering them a couple of £k+ above that.
You will likely get more selling privately, but I don't think it is that easy at the moment from the cars I have seen still available for sale.
I am looking for a good, low miles car to keep, I am a fussy buyer in no hurry, so have been following the market for a while!