Instead of slamming it down, or dropping it from 20/23/25 inches with 10lbs of force and whatever other methods the dealers tell you, just adjust it yourself correctly and press down on the hood at the location of the latches.
Both my 535 and M3 came with the latches and rubber stoppers not adjusted perfectly so one side would latch while the other wouldn't unless I pressed down afterwords with decent amount of weight.
So instead of dropping and slamming the hood, do as others have already suggested: adjust both the metal latches and rubber stoppers until you are satisfied with the way it closes by just applying some pressure on it after the center latch catches. Yes, it's a trial and error process and takes some time to get it right, but it's not rocket science and you'll have a peace of mind if you have an OCD for such things... as I do.
I can post a video if people still can't find this in the manual or understand how to do it just by looking at the latches themselves.