So, he went and testified and no harm befell your dad. The LACK of a bill of sale did no harm.I dont have a problem signing a bill of sale. I dont require one when I sell, but I do ask to see a Tx DL or LTC though. Why, you ask? A long time ago when I was a kid, my dad bought a ruger 357 single action from a FFL. It was blued and dad finally sold it and bought a stainless model. A year or so later, two detectives show up at the door, asking dad about the revolver. Apparently, the guy he sold it to shot a cop with it. Cops got the gun, ran the serial number, and linked it to dad. Dad had to go testify in court as to who he sold it to. There was no paperwork, so it was his word. Guy went to prison.
Buying and selling without a paper trail is fine, most times. It is just those very small number of times that it isnt fine, that really matter.