If the jury learns that Mr. Copeland was required by the rules of the gunshow to make his sale through an FFL; but that he violated that rule, they might infer that Mr. Copeland knew he was making an illegal sale.
The law is not based upon inference. The law is based on the deed and the intent through means, motive, and opportunity.
Gun Control: The premise that a woman found in an alley, raped and strangled with her own pantyhose, is morally superior to allowing that same woman to defend her life with a firearm.
"Science is built up with facts, as a house is with stones. But a collection of facts is no more a science than a heap of stones is a house." - Jules Henri Poincare
"Three thousand people died on Sept. 11 because eight pilots were killed"
-- former Northwest Airlines pilot Stephen Luckey