Earlier quoted context omitted.
I doubt it was silly. He likely offered you a deal that would have lost money if not for the financing.
Call me old fashion, but I think car salesmen ought to make their money off of selling cars instead of exploiting consumer's ignorance of financial tools and more complex math. This is so much more nefarious.
At what point do you expect legally competent adults to pay attention to and take responsibility for what they're doing?