Rear bumper lower and sideskirts are textured grey as per very base model cars, while the car itself is really well detailed. I think I had similar style wonderings from the interior too but with the pics no longer being there and originally only skimming my way across it, I cant remember what the specifics of those were.
I also think it's a car that floated its way around VIC having been repaired and in a 'nearly put together state' which I remember being sold to an interstate buyer, maybe back in 2018 or 2019 and it was sub $5k. It may not be the same car, but there were enough little details in the pics that made me suspect it might have been.
850Rs are way more desirable now than they've ever been, so I'm not saying $18k unreasonable, but I'd have some questions if I was going to pay that for the car.
There's some cars that are going for high dollars at the moment, so the market is obviously hungry for them.