The buyer bought a $100 bank note. Because he had chosen bank note signature, I didn't realize it was a fraud and thought he is a real collector. I shipped the item as registered mail, and when the mail arrived, he refused it and the mail was sent back. He pretended he was innocence and blamed Canada Post, but his suggestion that sending the item again without signature exposed his real face.
He must have filed other 'item not received' cases. Another seller left response to the original feedback to warning other sellers; In fact, his eBay ID was suspended by eBay and eBay did send me email to warn me, just too late, the item was on the way.
He now registered as another eBay ID n1ght_26 and used it to contact me.