It’s an old bike with lots of shiny “newish” parts on it. The parts may be worth some money but the frame is v-old
It’s a 7 year old frame (it’ll still trundle on for years baring a smash) with some ‘newish’ shiny parts, an up to date equivalent would would be a good couple of grand+… for £500 anywhere else you’ll not be getting that spec X0/XT/XTR Drive, Hope brakes, Thompson post/carbon bars, etc on a newer frame/fork with bigger headtubes or bigger wheels IMO… it’s not a bad deal.
ebay prices as a guide are terrible these days, people bid silly money because they get caught up in the bidding and don’t know the actual value of stuff…
The OP’s mate potentially has a bit more “Comeback” buying from a mate than a stranger on ebay, so you could say there’s some value for the buyer too.
£500 is a fair price IMO, I’d not quibble too much over a counter offer £475-450 though if it saved you ebay/classified nonsense, fees and/or postage faff…