Good character can be a subjective thing. Whenever guns change hands with no paper trail or documentation there is always the chance for ulterior things to occur. Your modus operandi
is admirable but why should the society at large trust you or anyone else to do the right thing just because YOU decide who is or is not a person of good character? I know, it doesn't really matter since guns are all over the place and even thugs have plenty of them.
But thugs do not generally go to churches or schools to commit mass murder. Further, the loser nerds who perpetrate those kind of killings are too afraid to go in to thug territory to buy their guns. Those type of killers usually go the legal route. typically they have no criminal record and appear to be just ordinary joes protected by the 2nd Amendment. Even YOu might have sold a gun to any of them.
It would be possible that someone with my sense of responsibility may have sold a weapon to someone like Adam Lanza's mother, but I believe she acquired her weapons by retail sales with background checks, records; the whole 9 yards.
Her son murdered her. Circumstances of that are unknown. Could it be that he killed his mother because she was trying to prevent the rampage her son was about to go on? Interesting twist, but it can never be more than a supposition.....
Other school shooters stole weapons from parents as well and yes, some purchased their weapons legally.
Those that purchased their weapons were subject to background checks. NONE, to my knowledge bought weapons from a private seller at a gun show. None acquired weapons that they wouldn't have obtained if all private sales were subject to background checks. Your proposals would have accomplished NOTHING but inconveniencing tens of thousands of sane, law abiding persons as they tried to purchase a legal product in a legal transaction between them and another person who had every right to legally sell a firearm.
SUGGEST SOMETHING THAT MIGHT ACTUALLY WORK.