nothing. If you are good enough in rendering, and you have a great cp which is powerful enough, i think you don't need to retouch your image.. well, i'm not virtuoso and don't have powerful cp but.. you saw the results.. nothing is impossible:)
I see, well, It was rendered with a great HDRI backdrop, I think it's a royalty free stock image, called "black studio" or the other name of it is "studio lightning". And the material is simply a high gloss stuff, in my case it is a black, metallic thing. It was rendered in Modo 401.