Trade in values

It is sorta like, "Pay more and we can allow you a higher value on what we take as your trade in". That said if what you have is a nice rig and well cared for and they figure it will sell quickly then their offer will go higher.
I worked at a retirement job for a few auto dealerships around town here - what they do and how they figured things was amazing but always seemed they made money on the car they sold you and the car you sold them.