General overall health of our bodies.
I myself have experience on training given at a "jewelry store" Training consisted of not even two weeks. You're shown the gun allowed to test on a fake head coworkers and friends. Then you have someone "walk you through" how to do it on a customer then you're on your own. ANYONE who is legal age to do so can be shown how to use a gun. People working at these boutiques also say using rubbing alchohol is a safe method of cleaning. It's proven to stall the amount of time to heal!
The first concern when it comes to piercing is sterilization. Any kind of procedure which involves contact with blood or bodily fluids requires strict adherence to cross-contamination prevention. Piercing guns are usually made with plastic and cannot be sterilized in an autoclave. Sure, they wipe it with alcohol or antiseptic in between uses, but how sterile is that? It is not unreasonable to guess that in a 2-week training course, these mall piercists are not being taught about infection control and blood-borne pathogens. A quick wipe with a sterile pad is not effective in removing disease-carrying blood.