Does telling the dealership I have the money and will buy right then and there help you get a better deal?

I was approved for a $12,000 loan and have a 96 Jetta GLS for trade-in. The car is in great physical shape however it does need a control arm repair(i hit a curb in snowstorm).



Is it easier to buy a car when you have financing already set and a trade in? Would it be unreasonable to make a offer of my $12,000 and my car for a car thats tagged as $15,000 on the lot? I would tell them I would be willing to buy the car right there on the spot.
The absolute best way to negotiate is to use the commitment close. By saying