Ok my fail. Let me explain this.
The perspective of the car is not the same with the background's (BG) perspective.
The wheels are not good. I don't know how to say. But try to take them on the original wheel. The reflections are.. there are no reflections. If you change the background usually you have to change the refs, too. Now you could make some building reflection. But it's not easy so keep practice on the easy things like: rim change, bg change, lowering, color change etc.. And if you can make these things perfectly then try more difficult modifications. Also the shadow is just a square thing. If you see another car in that angle like the bg you will see the shadow is smooth, not this square thing. Sorry for my bad english I can't tell it to you better.
The cleaning is quite good.
Keep it up, it'll just get better and better. Hope I could help you.