How are sales transactions typically done these days?

[Multimotor]

In this scenario, has an aircraft history been requested from the FAA? That might reveal things that could surprise the owner, since it's not unusual for paperwork to disappear over the years. It's cheap enough that it should be the first step if a potential buyer is at all serious about purchasing the airplane.

https://www.faa.gov/licenses_certifi...craft_records/

How about a title search? The aircraft history should contain all lien records, but often doesn't. AOPA can do that.