Denise, as others have said there is a tax savings because the tax you pay on the new vehicle is based on the cost of the vehicle LESS the trade-in amount, and that could be substantial. In PA, with a 6% sales tax and a $9,000 trade-in, that would be $540 of tax avoidance/savings.
Now, if you are CONFIDENT that you could get a couple of thousands MORE for the Trac by selling it third-party, and CONFIDENT that it would sell quickly AND without hassle, than there really is no discussion now is there. $2000 extra in your pocket vs $540 saved...$2000 wins every time.
But, just how CONFIDENT can you be that it will sell at that higher price, quickly (or at least in the timeframe you need), and without a lot of fuss? That's the gamble of third party sale, and why so many people will simply trade-in if the difference is minor.
Do you have the time (a few weeks to a month) and opportunity to try to sell it first? Is there a safe place nearby with high traffic volume that you can park it once it is all shined up, and put a 4-Sale sign and phone number on?
TJR