Remember when you purchased your rifle? You had to fill out paperwork.. show your license ect..

If you just sell it to someone and get the money and give the gun.. you bypass this process. Then there is no record of who the current owner of the gun is. Did you check to see if he/she is a felon?
What if they rob a bank and leave it their... when the LE checks the S/N they come and visit you.

I would have the purchaser pay the small, usually 30 dollar, fee to have a gun store transfer it to their name and then keep the paperwork showing this.