Clearly, health and safety issues are a top priority for the true professional. A lack of ego or defensiveness leads to a more available, honest piercer, who is willing to learn new things without embarrassment. Technical skill is acquired over a long period of time, but so, unfortunately, are ingrained bad habits. While the qualities that define one as being truly professional may be difficult to define, it is much easier to define an unprofessional piercer.
A giveaway sign of a non-professional is misrepresentation of one's abilities. If you were doing something well, it wouldn't be nearly as important for you to have some sort of fancy title or long list of fabricated qualifications. You'd simply do good work, and let your ability speak for itself.
When a piercing establishment uses term in their advertising such as "medically approved", or "medically trained", what does that mean? It can mean that one or all of the staff have taken first aid or CPR classes. Did one of the staff go to nursing school for a time, or work as an EMT (ambulance attendant)? Such claims should not simply be taken at face value. If they're making a medically related claim, ask specifically what they mean. If it's "too good to be true", it probably is. Medically-related training doesn't indicate skill as a piercer. Piercing is a very specialized skill. It may, hopefully, indicate awareness of sterility issues. Would you choose a tattoo artist who is a retired nurse, and cannot draw anything more complex than a stick figure?
If piercing-related training is being offered, be sure to ask questions about the provider's accreditation! What does the fee actually get you? Anyone can offer training and make whatever claims they want about their benefits. However, part of complying with applicable laws requires the provider to be honest about what exactly you're getting for those hard-earned dollars. Laws which apply to taking money for training cover other important issues as well. If they're not operating their "training" or "school" in compliance with applicable laws, what does that say about their integrity? Can they be irresponsible about the training, yet remain safe and responsible about the piercing services they provide?