The firearms I currently own come in at more than 60% private-party acquisitions. However... All but one of those private-party sales were from known-legal sources; coming into possession of a known-legal person. So, it doesn't really change anything from a 'questionable transaction' standpoint.
If I were to take into account the firearms I've sold, or traded, to FFLs or private parties, it may change a bit. But, I don't feel like hurting my brain, by trying to figure all of that out.
"Such is the strange way that man works -- first he virtually destroys a species and then does everything in his power to restore it."