https://www.vice.com/en_us/article/akee4e/someone-made-dollar3000-selling-3d-printed-guns-at-a-gun-buyback-event

Someone walked out of a gun buyback event in Houston, Tex. with more than $3,000 after unloading a box of over 50 3D-printed guns, according to local officials and media reports.

The “no questions asked” event was the first of its kind in Houston, offering residents Visa gift cards of $50 - $200 for each gun they turned in. So naturally, someone used a 3D printer and freely-available schematics to fabricate dozens of so-called “ghost guns”—and turned a tidy profit.