Hi, I have tried to tint the rear window of my Wifes' 500 yesterday. O picked up a couple of rolls of limo black tint from the car boot for 50p each. 2 hours and four attempts later I managed to fit some looking ok. It is her car so if she doesn't like I will pull it off but if she is ok will get a pr job done. I didn't do the side windows at the back as I thought it might make the kids feel claustrophobic. I like the look of it as the car is black anyway but hey it's not my decision....
Have a look at the bottom of this thread on my old 1.2 these were done by sa local tinting place in Mansfield, £70 all in superb job and a lot cheaper than the factory prices, looked as good when I sold it as it did when done 3 years earlier.
Made the back of the car a lot cooler inside on hot days.