I can't see where the presumption of guilt until proven innocent has a place in the Bill of Rights. Private transactions are perfectly legal in most states, if I understand correctly. ( Since I am in Kalifornia, everything has to be cleared by Gray-out Davis. ) Gun shop owners should not be forced to filter their clientele.
The idea that some felons have violent criminal records with a dozen convictions is sickening. The animal that killed little Polly Klaas had been convicted of kidnapping and sexual assault. He used a knife not a gun.
If a felon gets a gun and uses it in the commision of a crime, it is a threat to kill anyone who interferes with his criminal intentions. Such a crime deserves serious and increasingly severe punishment.
Nobody every walked into a liquor store holding a gun three times by accident. The third time we should be able to assume that such a person is too dangerous to ever be free.