Car Dealarship Database Design
the first diagram you can't realized in a rdms, you need to make sales always to an entity, to represent the relation ship.
if we take the third diagram, you would have all the wanted data, but you couldn't make foreign keys work, because of the ring relationship.( every row that is referenced mus exist before, this doesn't work in a ring relationship).
now you have two possibilities:

you have  to represent the trinary relationship in an entity, and you wouldn't have the eer 1 any more, as sales is an entity with foreign keys to all three tables(entities)
you put the relationship in your application code

the first gets you your second approach.
The second doesn't show the relationship with foreign keys, so you would add the information by adding comments to the tables.