What I see, and have run into, as an issue here is the term "trade in". The salesman says a person can "trade in" a camper... but then "charges" the person to pay off the old camper. That's not a "trade in" in my mind, that is paying off the old trailer, by folding in the cost with the new trailer.
It is really just semantics and word play, but you have to be careful to really understand all facets of the "deal" you are getting. Seems like tinstartrvlr was doing his homework in going over the "deal".
Believe me, I have been snookered with salespeople using shananigans with deals!