If you are buying a gun from an FFL, all Fed and State laws apply, gunshow or not.
A lot of States don't care if individuals buy/sell guns to other individuals. It is personal property being bought/sold. None of the States business.
My State of Maryland is not an example of this as all transfers of "Regulated" firearms (handguns and most assault rifle-ish things) must go through the State Police, forms, 10 day wait etc.