Social media platform rules on firearms
Most major social media platforms prohibit posting firearms for sale.
Unfortunately you can't post a GunTab Checkout button on most social media platforms, or even discuss a firearm transaction. The largest platforms strictly prohibit firearm commerce.
"We also prohibit the purchase, sale, gifting, exchange, and transfer of firearms,
including firearm parts or ammunition, between private individuals on Facebook."
(emphasis added; does not prohibit purchase or sale involving FFLs)
Facebook Community Standards: Regulated Goods as of 2019-03-01
"... buying or selling firearms ... (even if it’s legal in your region) is also not allowed."
Instagram Community Guidelines as of 2019-03-01
"We remove content used to sell or buy regulated goods,
like ... firearms and other hazardous materials."
Pinterest Community Guidelines as of 2019-03-01
"You may not use Reddit to solicit or facilitate any transaction or gift involving
... Firearms, ammunition"
Reddit’s policy against transactions involving prohibited goods or services as of 2019-03-01
"Twitter prohibits the promotion of weapons and weapon accessories [in paid advertising]."
(emphasis added; does not prohibit promotion in ordinary tweets)
Twitter Ads Policies as of 2019-03-01
"Content intended to sell firearms... is not allowed on YouTube."
YouTube policies on content featuring firearms as of 2019-03-01