In KY, what is the right way to sell a registered handgun to an individual.
In the first place: Registered? In KY, there is NO "registration" of handguns. The FEDS do keep records of Class III weapons though, so I presume you're not talking about a Glock 18 or equal. That yellow form you fillout at the gun dealer when you buy a gun at an FFL is not registration, though there are some naysayers that think it is. Really, its not. I also thought the legal handgun age is 21, not 18.
In the second place: with Federal Law, you cannot sell to anyone who resides outside of the borders of KY.
Beyond that, to my knowledge it's an open game. However, I do keep a record of who I sold my firearms to, including names, addresses and phone numbers just to cover my backside if the issue ever came up in the future of that weapon ever being used in commission of a felony. I recommend (again to cover your backside) that you verify they are a legal resident of KY.
I've wondered how one would know that they weren't selling a gun to a mental nutcase or to an illegal who are not supposed to have guns. In reality, you have no way of knowing stuff like that. That's one of the problems that I believe future Fed Governments will likely address.