He and his friends run a blackmail team. They look for subtle errors and ambiguities in the seller's description. Then place an order to buy. After receiving the items, they will leave bad feedback saying you fraud him.

Our description is comprehensive, so from the full description of the look. Normal people will not misunderstanding. Also never had any buyers reflected the problem.
For them, they only see that you have ambiguous words, Malicious misinterpret words meaning. And blackmail you, saying you are fraud. Claim they will report you to eBay, Amazon if you don't give him 10 times of the money as the item price.

Don't give them any money, lawyer up, fight against these people.

This is also a lesson to learn. When you describe your goods, please be careful to choose your words. Make sure they won't have any chance to be maliciously misinterpreted. Do not give any chance to these people.