A lot of these KM's would have had the sh!t drove out of them as people test braking, acceleration, cornering, etc ( I know I would).
I never bought a new Car but I thought they had to be drove sensibly for 1st few thousand KM to break the engine in.
Also 10,000 km in 5 mths seems to be a lot for a demo so Garage staff may also be using it and they would hardly treat it like there own.
I would be asking for 30% off and take no less than 20% especially in current market and the fact that they are desperate to get rid off it before year ends.
It less than 2 mths to will be worth up to 40% less depending on car. Good Luck.