Grew up around the car business and it's rare when someone comes in and says write it up, I will take it.
I've found being a qualified buyer in the eyes of a seller to be the first step. No sense wasting time if you are not a willing and able buyer.
Second is know exactly what you want going in...
Third is not to be a jerk.
Fourth it never hurts to ask if there are any specials, promotions, last year's model, demo, etc available.
One manufacturer was offering a new Husky chain saw and my friend also needed a saw... Dealer told him to come back in a couple of days the price of the mower would include a saw...
Realize, no two Dealers will be the same... brother wanted a loaded Honda Van and they were way over sticker around here... got on the phone and called a Dealer 150 miles away that had no market for a top of the line van and was forced by Honda to take at least one... he got a killer deal because Dealer was basically stuck in that market.
As a fallback, you can always ask if you buy... will the dealer throw in an extra set of blades, or whatever.
It's all about negotiating...