Do not pay with PayPal directly through Facebook/Messenger (unless they have changed their policy). The last time I looked at their policy, there was no buyer's protection. Have the seller create an invoice through PayPal and take screenshots of the listing and all communication, including the seller's FB profile, just in case. I have sold through Marketplace in person and by mail without issues, but that's where I saw that PayPal transactions are handled differently--no seller's fees are deducted--and that's why I searched for the policy.