In Georgia, a private sale of a firearm isn’t illegal, nor is there a requirement for a Form 4473, background check or a bill of sale. The only requirement is that the seller cannot ‘knowingly’ sell/trade/etc. a firearm to a person ineligible to own a firearm (a convicted felon, for example).
Pretty much the same way in Arizona - not so long ago, even States like the Peoples Republik of Kalifornia were like that. All it takes to lose your rights is a willingness to trade them for a meal from the government soup kitchen....