How to correctly buy a car that is already on credit?

We are planning to buy a car that is currently on credit. As far as I understand, first we need to close this credit (naturally, at the buyer's expense). Question: how to protect ourselves, how to properly formalize such a deal, and what documents are better to prepare with the seller in advance? What should be checked before buying such a car?

And what if I bought a new car at a dealership and didn't know it was on credit, and now bailiffs have come to me?

How can you even buy a car without checking if it's under lien? Did you sign the papers without looking?

Hello, please help me, I bought a car, and a year later it turned out that it was on credit, the seller hid this, and made a duplicate PTS as if it was lost and sold the car, now the bank demands payment or confiscation of the car, we filed a lawsuit against the seller, but so far no results, what should I do? where is justice
Thank you.