Great work, the perspective works and you've done a nice job using the select marque, here's a couple of tip's, if you are interested.
Copy the car layer (quick way is in the layers pallet which shows the layers stacked up, click and drag the car layer down to the icon that looks like a new sheet of paper not the bin on the right!) this is now laid over the top of the original car layer.
Then tint it using "apple (or ctrl on a pc) and B" to bring up 'colour balance' now move the sliders on mid tones adding some yellow and red till it looks like it's tinted slightly too orangey in colour.
Now on the layers pallet reduce the opacity to around 15% and set the layer to "linear" in the drop down box (it should be set to normal)
What this will do is tint the car layer you've just created and give it a slight hint of the ambient colour pallet found in the background, you can then use a soft brush eraser set to a low opacity (30-40%) and take away some of the tint to give a natural tone.
For basic reflections; Copy the wheels and pick some bits of the lower bodywork which catch the light and paste that, free transform it vertically, and line it up with the features on the car. Now set the layers pallet on this layer to "screen" reduce opacity till it looks natural and add a slight motion blur (option is in filters).
You could add another layer then using the stamp tool "s" and just fade in some of the tarmac in the shadow below the rear bumper to blend slightly.
The screen layer can be used to add windows (that have been removed) by replicating the reflections using the airbrush, black cant be seen on a layer set to screen hence why it's good for re-creating screens!
Keep working at it and you'll never even know it wasn't there.
For those who dont no me im Oldskoolbaby's brother and I just thought I would show you what I do in my spare time. Ive been using photoshop for about a year now and I think im starting to get the hang of it 
