Here's an example of someone (a retired police officer) who is now facing criminal charges for being in an unlicensed gun dealer. From July 9, 2012 CBS Miami:
Police say Jose Quintana, 55, sold the guns without any papers for at least three years at shows all over South Florida, according to The Palm Beach Post.
Quintana made his first court appearance Monday morning in a Palm Beach County courtroom charged with dealing firearms without a license. The Bureau of Alcohol, Tobacco and Firearms reportedly opened their investigation into Quintana’s alleged dealings in 2009.The definition that BATF uses is that you are not just occasionally selling a gun, but doing so with the intention of making a profit at it.
Agents found Quintana deposited nearly $108 thousand dollars into a bank account between 2008-2011, reported proceeds from gun shows in West Palm Beach, Fort Myers, Fort Lauderdale, Orlando, and Miami.Yeah, that sounds like he was making a profit at it.
Hat tip to Shall Not Be Questioned.