First go to FAA.gov find the page where they sell you a CD containing all the info about the airplane in question. it will have 337s, registration (past and present) and also lein paperwork on file. Cost about $10 last time I got one. Or you could hire a title search company and pay them about $100 for essentially the same thing.
Either way it will be the best $$ ever spent prior to purchase of the airplane.
I once found that I was about to pull the trigger on an airplane that had a lien on it, (10 years old) Found that it had changed hands several times since the lien had been placed. I told the seller about it, and he went off like a grenade. Understandably so, lien was for about $5k, and he'd just sunk a small fortune into it. We contacted the lienholder in hopes that it just was a paperwork error, and it had been paid off. No it hadn't been paid off, and the lien holder hadn't persued it because they knew the airplane was a dog. But they hadn't written it off yet either. "Oh by the way where is it?" We declined to tell them just yet, and proceeded to do their legwork for them.
Got the guy to pay off his note, and got a letter of release from the lienholder.
By that time I was over it, and the airplane had other issues, which shouldn't be there with an asking price of $40k, and the seller wasn't comming off the price. So I walked with an education on the worth of a lien.