Welcome to Android Central! I'm a bit confused--Factory Reset Protection usually requires you to enter the existing Google account information after an unauthorized factory reset (i.e., without removing the Google account before doing the reset). Have you been using this phone with the seller's original account still on there? Or has it been doing this ever since you got the phone?
Either way, the best thing to do is to contact the seller and explain your situation. If the seller is nice, maybe he'll tell you his Google account and password, and then change it afterwards. If he does tell you the account and password, then as soon as you're past the Setup Wizard, go to Settings>Accounts, select the Google account, and remove it. Then do a factory reset.
09-18-2016 04:24 PM