I sent the item, a brand new MX Master 3 to the buyer. I found it a bit dodgy since the buyer asked me to leave positive feedback, even before I sent the item. They claim they'll reciprocate; they'll leave a positive feedback to me, even before receiving the item.

A few days after they received the item, the buyer claimed the item is not working. I tried to help them by linking to Logitech's help document. I even sent them a gift receipt. They then proceeded to file a chargeback through PayPal. When I asked the buyer to send back the item for a refund, they threatened a lawsuit saying, "return the money or face charges in a court of law." They refuse to return the item.

Subsequent messages:

"then you will face charges in a court of law, to the maximum extent permited by the law."
"tempus fugit"