eBay

I have a situation where the buyer wants to return the item because it isn't what he thought. He thought the item was worth a 200-300 hundred dollars and so was happy to pay $20 for it (it's probably woth $50 or so). I said fine as I take things back...

What is the correct procedure when you're blackmailed by a buyer. He has sent me three e-mails stating 'provide me with $X refund or I will leave you negative feedback'.