CNN:

At least four people — three in North Carolina and one in Indiana — were injured after weapons went off at gun shows Saturday, officials said, at a time when there's been renewed discussion about private gun sales at such shows.
Dixie Gun and Knife Show attendees bolted, with at least one woman wiping out in the frenetic scene, after gunfire rang out around 1 p.m., as seen on video captured by CNN affiliate WRAL.
Police later explained that a a 36-year-old man from Wilmington, North Carolina, was unfastening the case of his 12-gauge shotgun on a table near the show entrance when it accidentally discharged. The man planned to sell the shotgun at the show.
The bird shot ended up injuring three people. One was a sheriff's deputy, who suffered a slight injury to his hand and was treated and released at a local hospital before returning immediately to work, said Joel Keith, chief of police of the North Carolina State Fair.
A 54-year-old woman from Benson, North Carolina, was being treated a wound to her right torso at a local hospital, and a 50-year-old man from Durham, North Carolina, was treated for an injured left hand, Keith told reporters.

This is how it happened:

A man identified as Gary Lynn Wilson, 36, of Wilmington, brought the 12-gauge shotgun to the show at the North Carolina State Fairgrounds and was attempting to remove it from its case when the weapon went off shortly after 1 p.m., police said.
One wonders if these people even know that guns are dangerous, that they are not toys, that they must be handled with a great amount of attention and care. But to be honest, I only want guns and gun shows out of the city. The country people are more than welcome to have as many shows, guns, and guns that just go off as they want.

UPDATE!

Two similar incidents occurred at entirely separate gun shows in the Midwest, one in the Cleveland suburb of Medina, Ohio and the other at the state fairgrounds in Indianapolis, Indiana. In Ohio, the local ABC affiliate reports that one individual was brought to a hospital by EMS, and in Indiana Channel 8 WISH says that an individual shot himself in the hand while trying to reload his gun in the show parking lot. That brings the tally to 4 victims of gun violence so far at three different gun shows during the country’s first Gun Appreciation Day.