A story circulated on Wednesday about Instagram subscribers who are using the service to sell their guns. The Daily Beast attests that the practice is “mostly legal,” and while Instagram community regulation is unusually tight, the gun sales will likely be allowed to stand even while less serious activity is banned.

As The Daily Beast reports, users are snapping photos of their arms and using tag combinations to flag them for buyers, such as #glock #forsale. Users then negotiate in the comments or trade contact information to firm up the deal. It’s worth noting that online gun sales are not at all illegal, and selling to someone without a background check is only illegal in certain states.

The practice may be legal, but it's interesting in that far more harmless activity has earned the banhammer from Instagram, especially when it comes to hashtags. Back in August, a long and incomplete list of Instagram hashtags that produce no search results surfaced on The Data Pack, including seemingly innocuous ones like #17bitch and #instagirl.

Instagram has proven to be very aggressive about policing what tags its users can unify under and cutting down on spam. NYMag’s The Cut reported back in August that the “hashtag czars” of Instagram will block searches for tags that are “generic” as well as ones that don’t “provide enough ‘high-end value.’” Typically, this is directed at users who place paragraphs of overplayed hashtags (#instagirl, #iphone) to troll for likes and comments.

But Instagram also cracks down on sexual words (#porn and even #foodorgasm are blocked) as well as tags associated with harmful behavior, like pro-eating-disorder culture (#thinspo and #probulimia). This is an unusually high level of hands-on policing for a social network with 150 million monthly active users in September. For comparison, Instagram is on the scale of Twitter, which had 215 million monthly active users around the same time.

Most social networks tend to avoid stepping on the toes of even the most controversial groups, despite being private entities where the right to free speech does not hold. Twitter responds eagerly to searches for the non-Instagram-specific hashtags above, including those about eating disorders.

Facebook carefully toed the content line earlier this spring in response to feminist groups’ complaints about hate speech. Facebook stated it condemns hate speech but allows “offensive content” and “distasteful humor.” Groups, pages, and more content on Facebook lets users openly assemble and share their love for porn, guns, and drugs. There are accessible thinspo communities as well as pages for those who “like” eating disorders.

While Instagram takes a harder stance against these elements, gun trading walks enough of a line that Instagram allows it. Some states do not require background checks for private-party gun sales, though background checks are encouraged by the ATF, and it is illegal to sell a gun to a known criminal.

Since Instagram facilitates only the advertisement of the gun sale and not the transaction itself, it may be peripheral enough to avoid any negative involvement. Simple photos of guns are not a controversy the way a pornographic photo is. And as long as sellers take care to keep the sale legal, they will be OK too.

Update: while #foodorgasm appeared on the original banned tags list, Instagram appears to have re-sanctioned it. Likewise, #thinspo has been reformed into a searchable tag with an interstitial advisory warning.