If the buyer is out of state and not in some people's republic like Kalifornia, NY, or IL you'll need a signed FFL copy from the person receiving the rifle/shotgun. Then you can ship the gun to them. Make sure that you bring the signed FFL along because the shipper may well want to see it especially if it's not being shipped to a place that is not obviously a gun shop by name.
If the buyer is in state in most states it's not a problem, and unless you live in a large state where the drive might be impractical you might meet someplace halfway and transfer it in person. That way you won't have to worry about shipping damage or theft which can happen even in the best of families.