I need some advice with purchasing a used vehicle from a car dealership...?

I have found a Lincoln Aviator with VERY low mileage that I am interested in buying. I did the Kelley Blue Book research on it. If I don't want to get ripped off should I be firm with not paying anymore than what the Blue Book price states. Or is there a percentage more of the price that I should expect to pay? I know car dealerships love when women walk in. I have plenty of money to fund this but I just don't want to get taken. GUYS.....(and girls if you know about this stuff).....Please advise...