Its like anything in life. Something is worth what someone is prepared to pay for it. The more exotic, rare, pristine the item the more it will bring. Cars are no different.
What i dont get is salesmen being arrogant. The best deals are surely ones where both parties walk away very happy. The garage i got mine from noticed when my dad dropped me off to collect rhe car he was looking around. The salesman gave me some £100 vouchers and said if he is considering buying something come back and see him and i will get £100
Ps i have just bought HR 2008 63k miles for £10200. Didnt get a penny off but did get the bonnet and bumper respray throw in due to usual stone chips so worth a few hundred