By European Union laws, any country is allowed to open any product coming into customs that they have high suspicion of the content. Thus, shipping an item that weights 1-5kg and marking it way way down on value; like a $1000 booster box being claimed to be only worth $100 is 1) tax evasion, 2) your own god damn fault for trying to evade taxes.
Customs are god damn well aware that we, Europeans, do imports using false value declarations. A wrongly filled package slip is mostly the cause of this. Trying to think you can by-pass these trained professionals to win a few euro on import fees is tough luck and your own fault if you requested the seller to do so.
That said; File a complain, make sure you have a valid, clear invoice of the purchase and claim that the customs opening it has destroyed the value of the booster box. It’s worth a shot, but you never know with Germans ¯\_(ツ)_/¯
Slightly bounce on this one…
Customs on Amsterdam Schiphol Airport (AMS) and Athens Eleftherios Venizelos Airport (ATH) are the same. All electronics larger than a credit card have to be put into a separate bin to be checked (so; phone, tablet, laptop, game console, dslr). Not doing so will trigger the employee that you’re doing it wrong. It’s not just the Germans. It are the Dutch and Greeks aswell, even if you’re never leaving Europe, they push these crazy post-911 TSA pranks on everybody.