Package the item well in a sturdy box, take it to the PO, ask for a customs form, fill it out. They will attach one page to the parcel, and give you a copy. You then pay. The parcel is then sent. That's worked for any international parcels I've needed to send. Only difference is, I have the customs forms at home, so I can fill them out before going to the PO to save time.
Given that Germany can be a bit suspect at times (delivery can be quite slow), I would definitely add insurance, given the price the items are selling for. I would also add signature on delivery. Yes, it increases the postage costs, but you need to cover your butt.
Make sure you have photos of every square millimetre of the item before packing, so the buyer can't try and pull a swifty on you, saying it has arrived damaged.
