If your thinking is "yes, I'll make money by selling firearms (components) to people looking for a cheap untraceable gun", then you've basically decided you're

If your thinking is "yes, I'll make money by selling firearms (components) to people looking for a cheap untraceable gun", then you've basically decided you're comfortable with the risk of being found guilty of accessory to murder, in order to make a couple hundred bucks. Because of course "untraceable" doesn't mean the person you sold the gun to can't tell the police who made it, for instance in a plea bargain. That alone puts such business far, far outside the comfort zone of any normal 3D printing hobbyist.