Use a credit card in conjunction with your paypal account. On top of the protection from paypal, your credit card company can help you reverse the charges in the case of fraud. If you don’t have a credit card, open a bank account with a visa, or mastercard debit card. These offer the same protections as a credit card. Don’t use a balance funded paypal account. Move the money down to your back account, and force paypal to use your credit card.
Don’t even bother threatening the seller. Just file with paypal, and the credit card company. Emailed threats are of no use, just get your money back the second you try to log on and the password has been changed. You won’t get your money back instantly, but you will get it back.