I have attached a picture from my 71 GS that is all original. As you can see the type of factory screws that attach the data plate. They were not riveted From looking at the picture you sent, the screws are not factory correct. The paint code is 18 which should be charcoal mist. Now according to the production #'s 565 72 Riv's were painted black code #19.
You state the vin has a "W" in the vin, but the seller has not provided you the engine code. The engine code for 72 GS should be "WA". I also noticed the engine appears to be black when it should be red. Someone has also messed with the fuel line as I see a separate fuel filter, but no fuel line.
I'm surprised that no one caught that the front bumper is from a 71 as the 72's had the white rubber strip.
IMO, there appears to be many discrepancies, that the seller may be trying to sell you a fake GS. Being that you live in Europe, I would hate for you to get scammed.