with the background image I think you may just get away with flipping the image, failing that you could just use a sky or a different image.

As regards to the dark spots on the draws - it looks like its a reflection of the box on the ground (going by the prev image as you made it hard to see in the image).
Do some test renders with the box there and with the desk by itself to nail it down where the problem has come from. If it is the reflection you could just turn it down. - Or you could just use light linking and add a light just to effect that area -but I am not the greatest with V-Ray but I am sure that option still works.

Just some ideas for you. Again great work.