I noticed a couple of weeks ago a dent (very shallow like a small door ding. Half way up the black glossy trim near to the drivers door glass. It annoyed me so just bought a new trim piece at £45 from my local dealer, which i will fit myself at some point.
I suspected that this may have been caused due to hot sunshine and the trim flexing and distorting against the fixings behind. I looked at 3 Golfs at the dealers and I noticed that 2 of the 3 had similar dents on this plastic trim. Coincidence? Possibly, but I think not. I never touch this black panel to close the door as I know how prone they are to swirl scratches. Also, I always wash the car myself.
Take a careful look in the bright light - I suspect this could be a part / design flaw.