I agree with every other post here. It's also one reason why trading isn't always a bad option.
I know, I know - you can get more selling outright, or can you? You sure get more grief. :B You also need to look at the numbers, the REAL numbers, and it may vary depending on your location.
In NYS we pay sales tax on the trade difference. If the dealer offered $50,000 as an actual cash value trade number, you'd need to sell it outright for at least $54,000 to break even. What is the value of the grief you're going to get? Only you can determine that.