. >> this is armslist, it's the largest online gun site in the country. >> i'm looking for a cheap handgun for around .150 and $250. he's laying the money on the bed. this is completely unregulated. anyone can buy from a private party here without going through a background check. private sales can be completely anonymous -- no id, no background check, no records. >> critics call this the "private sale" loophole, an estimated 40 percent of gun sales that are largely invisible. >> we'd been told that south carolina's weak gun laws contributed to its high rate of domestic homicide. so our crew took a hidden camera to a gun show to see if buying a gun illegally was as easy as sources said. licensed dealers are required to run federal background checks and keep records of sales. we'll stop at a private sellers table >> what's required for the purchase, what do you need from us? >> show me you're a south carolina resident and show me some money. private sales between individuals must be done within the state. >> within the state? >> i can't cross state lines. >> this is $325 and this is $600...