And what if the firearm has a serial number (either before sell or not) - the seller has still violated the law but what about the buyer?He's not asking if he's the manufacturer, can he sell the firearm, he's asking if he is a buyer from somebody else that made it is it illegal for him to possess. It is already established that the seller is violated the law but what about the buyer?
Is there any legal requirement to 'register' the s/n?
If the buyer sells it again, what about new buyer?
Even if no legal problems for a buyer, could the firearm be confiscated?