If you find a lien, the best way to complete the buying process is to ask the seller to pay off the loan. Go with the seller to the lender to make sure they pay off the loan, and the lender can transfer the title to you once the lien is clear.
In case the seller can’t pay off the lien, you can take out a loan and let your bank know it’s to cover a lien on a car. Of course, that will create a new lien on the vehicle, which might be more of a headache.