Well, it starts with enforcing law. When you say loud and clear to somebody if you're going to carry a gun illegally, we're going to arrest you. If you're going to sell a gun illegally, you need to be arrested. If you commit a crime with a gun, there needs to be absolute certainty in the law.
You can sell a gun illegally in every state
( z1 possible :ARG1 ( z2 sell :ARG0 ( z3 you ) :ARG1 ( z4 gun ) :ARG1-of ( z5 legal :polarity - ) ) :location ( z6 state :mod ( z7 every ) ) )