This is the easiest thing you can do to put your car at the dealer's . choose another car then pay the difference in price to the trader in this case you pay taxes just for the difference of price ,but the problem is that the dealer will offer you a very low price that you deserve much more than it. Any way this is how dealers make money.
You can offer your car to lots of dealers & sell it to the one who will offer you the highest price even if you don't want to buy a new car & you just want to get rid of your old one, but to have to know that selling your car privately will help you to have much higher price specially if your car is attractive.
There are two kinds of buyers some of them may bother you for weeks asking you to cheek your car & complain about price. others will give you the price you want very easy from the first look at your car you'll be very lucky if you sold your car to the second kind of buyers.