Err much more than that.
Your car must be low miles with decent spec 
£10k must be well under the 4 year GFV, surely? I'd expect about £13-14k p/x on a 3.5 year old GTI PP, and expect them to be selling it for £17-18k.
Let me know when yours is 42 months old, I've got £10k waiting in the bank for it. 
A friend’s r was nearly going back to dealer for just shy of 9k granted it was a 14plate but dealers always try offer way less than market value
Yes, they always try to low ball you to increase their margin on selling it (maybe 25% markup for them vs what they gave you for it). While you're under the confines of PCP though, if they try to offer you less than GFV for your term, you'd hand the car back and start afresh with a new PCP. £9K for a 6 year old R seems a little low, but at that age I doubt the VW dealers are too interested in it being on their forecourt - probably got shipped off to auction.
I got £17300 for my (then) 46 month old R manual with Prets through an indie, best offer on table with local dealerships was £15500. However- I still had the remainder of 5 year extended factory warranty left, which was a big incentive for the Indy to pay what they did.