The point he's making is it's secondhand, if someone buys it & should it go wrong 5 minutes in to a game, it can't be returned to the shop for repair or replacement.
Same goes for usage, anyone can say "never skirmished" etc, at the end of the day a secondhand buyer is taking all the risks, so expects to pay a price that reflects that.
For years the generally "agreed" framework for s/h pricing has been 65-75% of the current cheapest rrp.
So a ballpark figure for yours would be £287, clearly something you probably disagree with.
End of the day your free to ask what you like, but don't be surprised that people comment or you get a mention on Macks.