Do make sure to give MM all the information you have on the seller.
I recently signed up as a seller and they required me to have a photo of myself with my ID, a separate photo of the ID and a photo of myself with some of my animal's habitats. At the very least they will hopefully keep the name on hand as a banned seller. Unfortunately that doesn't stop them from having someone else sign up as the account holder =/
Regarding Paypal:
Please tell me you paid via invoice or as a G&S. Do start contacting paypal regarding this now to file the dispute.
If this person convinced you to pay by friends and family, then you are out of luck. Paypal will not file disputes on friend and family purchases.