OK, that screen shot shows what I was talking about. There’s nothing behind the camera, so when someone puts their car in that scene, and if that car has any sort of reflection, which I’m sure it will, its just going to reflect the world color/texture. Model some extra buildings and sidewalks back there so that when the car paint is reflective, it looks more realistic.
You might just fake those buildings by setting up billboard cards or shapes which resembel stuff. Cause you will only see the reflections and not the geometry and every extra vertice will mean extra calculation time.
Maybe even just build a skydome to which you simply add a hdri or enviroment map.