Over the last few years I have made a habit of stating right up front I won't pay admin fees, I don't want and won't pay for etching, Scotchguard, nitrogen or anything else not supplied originally by the manufacturer.
At that point they can decide if they want to sell me a car.
Also I love when they send me in to see the "business manager" or secondary salesman, or the bad guy who told the poor salesman they couldn't possibly pay that much for your trade in..
Again I start off with, your salesman has just spent the last couple of hours convincing me this car is the most technologically advanced, safest, most economical, efficient and quality built vehicle in the world. Despite this you have just tagged on an exorbitant sum to re-check this vehicle was assembled correctly, how can I possibly need under seal, paint protection, extended warranty etc.
Generally they just grin and say "sign here", at which point ask for the free mats and tint job