​RE: Paying For a Vehicle
Let me add one other caveat to this thread.
In addition to the money transfer is also the transfer of title on a
vehicle.  Any time I have sold to a private party I have gone with them to
the local vehicle license office and done the title transfer right there,
right then.  That avoids any problems down the road if the vehicle is
involved in an accident, used in a crime, abandoned by the side of the
road, etc.  The title does not get handed to the buyer, it gets handed to
the clerk and the transfer takes place while I am standing there.