CYA: Best way is to have a state leo run the vin numbers for you. Call the PA authorities and ask em how to get that done. Clean title in hand and if you must, a Bill of Sale, belly up to the NY bar and give the state her triple dip.
Trust the seller? Have the seller sign the Title over and ride home on his/her plate. Bill of Sale? asks the tax clerk. "Lady here's the title, I paid x grand for it." Mail plate back to seller.
