They way to win is to sell your old rig yourself. The dealers play the game of inflating the value of your trade because; Most people have an inflated opinion of the value of their rig so the dealer has to meet the expectation of most customers. He inflates the value off the bat so people do not get their back up. This is called salesmanship he is after all trying to make you believe he is your friend. You will never buy something from someone you do not like.
Your rig may be worth less than NADA to the dealer because of many factors including time of year, brand of rig you are trading (to high or low end for his business) or even the age may be older than he wants on his lot.
Now to buy;
you find the rig you are interested in
When you know the rig you want, the price you are willing to pay and the dealer you want to buy from, do the following;
Put your name, address and phone number on a piece of paper.
Head to the dealership.
Inspect the unit you want.
Turn to the salesman and say the following words; "Here is my name phone number and address I will pay you $xxxxxx.xx for this rig plus tax and registration only provided it passes predelivery inspection. The answer from you is either yes or no. If it is no I will be leaving the lot. I have made you a reasonable offer now go do what you want to. I will wait here for 10 minutes. Let me know. If he comes back with anything but yes LEAVE THE LOT. If your research was good you will get a call from the dealer. MAKE SURE he is calling to agree to your price,if he is go back to the dealer to sign papers. If at this point he tries to change the deal then you DO NOT want to do business there. You will never have buyers remorse if you purchase this way because you payed exactly what you wanted. You should never try negotiating with a dealer. He is a professional at it and you are not. The dealer ALWAYS wins in a negotiation.