The plot thickens...
I found your engine on eBay and it's sister on YouTube. A stretched Mikado that looks very impressive.
eBay 2-10-2
Yes, they look like they are a business to give access to Russian consumers on US eBay sales, I would assume they re-ship the items too.
Bay.ru
It's a pity it came to grief. You should be able to verify the date he received the shipment from you which would raise the question if there was damage at that stage why didn't the buyer make a claim then?
I have never bought or sent anything to Russia but from what I have read damage is common and insurance is not always available.
Particular shaped boxes get punished especially if there is some weight in the enclosed item. Long boxes get dropped on their end so there can be much 'shunting' and shock within. No movement and foam padding at each end helps.
I hope you sort it out as it is not fair for someone to pass their problem on to you if they were shipping it elsewhere. It seems the world is all too full of asshats like that.
Andrew