As it stands today, unless I am somehow negligent in my sale of a firearm, and unless the issue of intervening or superseding causation is somehow taken out of the equation, I'm already not liable for the acts of a (criminal) third party. It's not much of a carrot if you're giving me what I already have.
Apples and orangutans. To use your traffic example, what you're talking about is holding a person "both legally and civilly" responsible when some
other person (to whom the first person sold a car) runs a red light and causes an accident.
No, they key is to not have registration. Yes, we register cars and homes. Those other records of transactions (bank records, credit card statements, store video, etc.) are not "registration" with the government.
Two quick problems: (1) Serial numbers aren't standardized, so if you want to tie a particular gun to a transaction, it's going to have to have make and model, too. (and that might make it registration?) Otherwise, a sale of a Glock with serial number BADID5050 may well get mixed up with a sale of the Colt Python with serial number BADID5050.
(2) If you're talking about criminal liability, you can't make the defendant (the person said to have sold the gun) prove anything. It's the State's job to prove the crime, not the defendant's job to disprove it.
Who says we don't want to solve the problems?!? We want to solve the problem of violence every bit as bad as the antis. We just have radically different ideas about how to go about it.
You can't hold someone criminally liable for not being able to disprove the allegations against them. That's not how that works. That's not how any of that works!
The history of negotiations with the antis has been a history of give-and-take. We give and they take. The antis lie about what they want to take and lie about what we give up. You cannot expect to be able to negotiate with them in good faith. History shows us that they do not expect to negotiate in good faith with us.
A little light reading on this issue:
https://thelawdogfiles.blogspot.com/2010/09/ok-ill-play.html