WASHINGTON (NEXSTAR) — Facebook says you cannot use the social media platform to sell guns. However, that’s not stopping private gun sellers and gun buyers from connecting on the site.

Here’s how it works: The gun seller posts a photo of a gun box or gun case at a price far higher than it should cost. The seller then invites a private message from interested buyers, who find out that the case or box includes a weapon, ammunition or other items prohibited for sale by individual users.

“I found one for a gun case for over $1,000 and when I clicked on the description it indicated, ‘Private message me for details,'” NetChoice President Steve DelBianco said. “Well, that was a sign that there was something more in that gun case.”

DelBianco said Facebook allows licensed gun dealers to advertise on Facebook, but since 2016, has ruled private gun sales are off-limits.

“[The seller is] allowed to do a private sale of that gun, but he’s just not allowed to do it on Facebook,” DelBianco explained.

Jonathan Lowy with the Brady Campaign said Facebook is endangering the public with the ease of access to guns.

“It’s just far too easy for dangerous people to get guns,” Lowy said. “People will be killed as a result unless they crackdown on what’s going on on their site.”

Lowy says Facebook’s marketplace is a way for people to avoid background checks.

Amitai Etzioni, a social scientist at George Washington University, said the loophole in Facebook’s marketplace is just a drop in the ocean.

“Even if nobody would sell another gun tomorrow and nobody would buy another gun tomorrow they’re still all over the place,” he said.

Facebook asks users to report any violations of the rule against private gun sales in its Marketplace and DelBianco says if you see something, you should say something.

“Ultimately these platforms rely on many cases on us,” DelBianco said.

A spokesman for Facebook said, “If we catch someone selling guns, we will take immediate action.”