It seems to fluctuate, I've been late on copies in the past 12 months for between £250 and £350 in nice condition. I've had a few folk pm me asking me to make an offer and it seems over £400 is what they want and in one case way over that.
Does the fact that 3 or 4 people asking for it at roughly the same time drive up the value so much or is it greediness? (Not having a pop at anyone there by the way). I know when selling we all like the best deal but I'd like to think there's an element of fairness that exists, there certainly has been with 99% of my purchases.