Many moons ago a friend happily told us that she traded in her car and purchased a newer one, and it saved her $25 per month!
She had 2 years of payment left on her old car, but the dealer cheerfully rolled the balance into her new loan, which was for 6 years. Yup! She saved $25 each month.
I started to explain how math works, but quickly realized I'd have better luck convincing a brick wall, so I shut up.
In the late 80's I knew a service manager for a VW dealership. He told me that people would have 3 to 5 year loans, but trade the vehicle in after 2 years, adding the old loan to the new one. Folks had $25 K loans on a $10 K vehicle ...