O.K I went out today, and found the slickest black car I could borrow from a friend, and tried to prove my point about black paint, time of day,and get away from the car......and you have no polarizer just sheer will power to take cool pics of your black car without reflections
Shot with my Iphone/no adjustments of any kind at 4:15pm while the sun was still up. I picked a location that was pretty open,but still wasnt perfect(30 yards open gravel to a raised road and some trees and telephone poles)
OK Iphone pic:
Now my second shot was shot with no processing either,but with a real camera(no post work except converting to Jpeg) This pic shows how great moving away from your black subject(I think this was about 100mm maybe 120mm) with killer natural light(around 4:45 by now)
Ok now this is just the stupid way, and how I usually do it....Two sb900's on boom stands,but the sun has set behind the trees so you still get a cool natural horizon line(again no photoshop trickery, and this time I was probably around 70mm)
Just remember when you park the car, and you look at the side of it what you see is what the camera will see. Try a slight angle to the sun to create nice horizon lines earlier than what I shot these, adn you can still pull it off in harsher light. Also dont forget even if you can get the black in the shade of a alley...across the street might not be in the shade causing some crazy reflections....always look before you shoot