I just had to get my car weighed again on certified scales to get compensated for a work move.
I did this same weigh about 12-18 months back, and the car came in at just over 3500 flat--but I was nearly empty (fuel light on, as it always seems to be in this car).
This time I wanted to make the weigh as "standard" as possible so I put EVERYTHING in the car: I was fully topped up on gas, I filled the windshield wiper fluid reservoir to the brim, I even (perhaps unnecessarily) put my manual back in the car and put the German first aid kit and warning triangle set back in the car (I lived in Germany for a while and these came standard with the car, so I figured it was the only fair way).
I weighed in at 3590 lbs, no driver. I have a MY 2012 E92 M3 with all options ticked off except sunroof, M Performance Exhaust, DCT, and premium sound.