I am very sorry to hear about damage you incurred. I ditto what others said, offering a calm, polite and factual explanation of events, will get you a long way with most folks. But the fact is If he had done a few things differently the bike would most probably not be damaged. Though my experience has been that Germany, Australia, the Swiss's post auto and a few others offer more reliable Post service. The seller still has recourse to file a claim and recover partial or entire funds. International carriers pay claims from insurance based on packing material, period. 2-4" of material around the item? Some state 2", some require 4" This becomes your baseline as to the sellers responsibility and ultimately the sellers liability. In order to help the seller with the claim, retain all the materials and box. If you can reconstruct the bike in the box with materials and take photo's it could help you to receive a more speedy settlement. In one case recently I had a seller tell me his bike shop did the poor packing job which caused damage to a bike I received. The bike shop paid me off so you may find a few different angles like this one.
Chris
Plunkett
Chicago, IL, USA