I have made a Max 7 scene that you can download and look at the materials of the car for glass or paint work. You can replace it with your own car and render.
For mental ray to render your scene nicely, you will have to have light source in the scene and enable 'Final Gather'.
see attachment 'draft FG render' for settings on draft work, the lower the 'Samples' are, the quicker it will render, but of course the quality is corse. Better to render drafts in 320 x 240 size.
Once you happy with your set up, see attachment 'quality FG render' for quality renders. the higher 'Samples' for the better quality, but will take very long to render.
see attachment 'environment background'. That is where you change your background colour or put an image.
here are 2 renders with reasonable quality FG setting
Yes, the petrol station was a paid project for a client. Took 7 days (normal working hours) to model, textured, lighting set up, camera walkthrough and render the animation sequence.
Don't get luxuary of much time in reality. Pressure was quite high, so can't do everything in high details.
Have you turn the glass material's tranparency setting right down? 100 is opaqe and 0 is transparent.
The image seems to be a bit washed out, what light did you use? may be the light is too intensed? try use only 1 Sky Light instead and try.
Here are some images I done b4 in Mental Ray with Glare effect long time ago. No Photoshop work needed.
The set up was 1 sky light for overall lighting, and 2 spot lights per each car's head lamp with little amount of volumetric light effects.