You would then be in violation of IL State Laws which state that a written receipt must be issued for every sale of a firearm and said receipt must be retained by both the buyer and the seller for a period of seven years.
Said receipt must also include the serial number of the firearm in question.
Therefore the correct response to an armed agent of the State showing up at your front door is "Do you have a warrant?"
L
Thankfully, and by no accident, I am not subject to IL laws.