Many states like Florida and Virginia provide their own background check systems as a substitute for the NICS check with federal approval. The reason they do this is that they charge a fee that generates an income source and state jobs as opposed to the federal NICS check which is free (thanks to the NRA).
Any person who knowingly transfers a firearm or ammunition to a prohibited person also commits a federal crime.
Not according to the Brady Campaign to Prevent Gun Violence
Virginia: State law requires gun buyers to go through a state-based criminal background check in addition to the federal NICS check. This is the best system since it includes checking both state and federal records to prevent criminals and other prohibited people from buying guns.