eBay (at least here in the US) has generally helpful support. I called to ask them about a deal where I purchased counterfeit Sony Ericsson Bluetooth earpieces, and the guy on the other end gave me some sound advice. YMMV.
Negative feedback is not your only recourse. You can file a dispute with eBay and they will require that the seller respond. They encourage you to work it out with the seller, first. If the package was insured, then the seller should be able to claim on the value of the item and refund your money.
And you do need to act fast. The burden is not on you, the buyer. It is on him, the seller. He needs to just make the claim on the package. I'm not sure how German Poste works, but an insured package should have some kind of tracking so as to prevent fraud.
But he might be pulling your leg. Give him a dead-line to either have the package presented or refund your money. If he does neither, file a dispute. If you paid via PayPal, file a dispute with through both eBay and PayPal. Don't let him give you crap about waiting for his insurance claim from the post office; that is frankly non of your concern.
If this sounds harsh, it is, but you have to protect yourself from losing your investment. And as a seller myself, this is how I would proceed.
Good luck. I'm sure others will have some advice and probably point the blame at you for doing business on eBay. Tell 'em to sod off :-P I have over 500 transactions on eBay and only two have been bad.