I HATE car dealers/salesmen. Just based on the “nitrogen” issue alone, I’d walk, but the whole thing sounds shady to me.
Should You Fill Your Car’s Tires With Nitrogen?
The Green Cap on Your Tire Could Take Green From Your Wallet
http://www.edmunds.com/car-care/should-you-fill-your-cars-tires-with-nitrogen.html
I specify 80% nitrogen.