Not trying to rain on your parade but any time I dismantle a truck, I toss the old brakelines into the trash, regardless of their condition.
Whether they leak or not, I would never sell used ones to anyone for the sole reason to liability. Sure they may not leak and worked just fine for you until you tore it apart, but over a short time they can dry and crack which can lead to pinhole leaks and someone losing their brakes. You can imagine the rest.
As I said, not trying to put a damper on your deal but just an idea and opinion.