Unfortunately I can tell you, they will low ball your car like nobody's business! So don't expect the price they offer will be even close to the normal market value, doesn't really matter much first hand or subsequent owners, that's how used car business wants to make as much money as they can. They can low ball you as much as 30-40% or even more below market price, depending on what car you want to sell. So the key is to just focus on the delta price that you need to top up, as long as you can nego for that delta amount to be reasonable for you then can go ahead with the deal but you also have to bargain hard and don't hesitate to low ball them as well coz used car dealers make a lot of money like that.