Well yeah
I'm not sure what I was hoping to hear back.
It is the render that makes it look realistic, but the geometry is very important, especially in a car render where the realism of the car is in how well they fake the light reflection. You can control some of the light reflection with the materials, but the curves of the car is really what suspends disbelief by physically throwing the light.
My professor from my animation degree worked at a car commercial studio where he worked on 3D cars.
So... in short, I guess what I'm trying to say is... you can't polish a turd.
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