I'm no lawyer, but if I go to the Cal DoJ website (https://oag.ca.gov/firearms/certified-handguns/search), this is what I see:

As of January 1, 2001, no handgun may be manufactured within California, imported into California for sale, lent, given, kept for sale, or offered/exposed for sale unless that handgun model has passed firing, safety, and drop tests and is certified for sale in California by the Department of Justice. Private party transfers, curio/relic handguns, certain single-action revolvers, and pawn/consignment returns are exempt from this requirement.

But you may be right, there may be OTHER rules that apply to private party transfers.

marky-d