Tips on Buying Cars: trade ins, true numbers, hot buttons

Question
I am about ready to buy a new or slightly used auto.

I have read a lot of advice trying to do the best i can.
All of the advice was to not mention that you have trade in until you are set on the new purchase.

However, if you have used Edmund and Kelley you should know what your used car is worth and more research will tell you what the new car should cost.  So, putting those two together, a person should have a good idea of what they should pay.So, what is the advantage of not mentioning the trade in out front?

Thanks

Answer
You accomplish one thing at a time. First being what you are going to pay for the car. Here is how it works; I become your trusted salesman, I ask you questions like, How did you hear about us, did you find us on the Internet or did you see our ads. I want to know how much knowledge you may have about price's. Then I ask do you have a trade in and is it payed off (what difference would that make)
I can figure out how much to offer you for your trade to satisfy your mind. A car for sale has about $3000 mark up, the avg profit at a dealer is about $700, they use the rest of the profit ($2300) to make the numbers look good but we have to know what your hot buttons are. If you want $4000 for your trade and it's worth $2000, I can take $2000 from my profit and add it to your trade in on paper and still make $1000 profit but I would have to keep the price of my car at sticker price. By making a deal on my car first and I have no idea you have a trade, that when you do suprise me with it, I can only give you true numbers of your trade value, if you then tell me 'I'm not getting enough for my trade,I want more"the only place they can get it is by truly putting real money into it.
 Dealers train their people to work a 4 square, it's like Tic Tac Toe, Price of the car,Down payment,Trade value and last but not least Monthly payment, It's like the Peas in a Cup Trick, they keep moving them around until you agree on the monthly payment. You need to work the game one step at a time. Don't feel pressured,keep saying I want to know the price of the car first, no I don't have a trade, I don't know how much I want to put down. Use payment calculators from some of the web sights you mentioned so your familiar with payments and rates. Anymore questions just let me know.