yeah, you've almost got to put your foot down to just working out a price for the vehicle before even talking about a trade in...try to keep the two things as separate as possible for as long as you can
sometimes i wonder how well it would work to go in and haggle over a car you don't want, get a good trade in quote and a bad price on a car, ask them to write out the numbers for you so you can think it over and walk away with no intentions of buying.........then come back later, work on the price of the car you want with a different sales guy and when you come to a price you like for the car then be like "sounds good, and you guys offered me this much for my trade in last week, you'll honor that quote, right?"