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I tried googling this but most answers that came up were regarding "cash" as bank deposits that a check is normally issued against. Not "cash-cash" or physical cash, as a bunch of bank notes.
Say one were to buy a $200K home or a $40K car in the U.S. but wished to pay in physical cash. Is it even legal past a certain amount? What kind of scrutiny can (s)he expect from regulatory agencies, IRS etc. if such a transaction surfaces up?