I understand that in massage school, there are hours and hours of class time spent on talking about ethical practices while performing massage. There are ethical practices involved in doing Reiki also, although I would make a bet that very few Reiki Master Teachers are actually giving much class time to this topic or even bringing it up or so I've heard through the grapevine.
So what are the ethical practices involved in being Reiki Practitioners? Going back to the five Reiki Precepts "Just for today, do your work honestly" (depending on which translation you're reading". One unethical practice involving Reiki would be for a Level I or Level II Reiki Practitioner to, first all do Reiki on the public and charge for it at all, but if they do, to charge the public the same amount for their doing a Reiki session on someone that a Level IIIa (Reiki Master - the level at which you are certified to actually treat the public) or a Reiki Master Teacher would charge (Level IIIb). Because you are not opened up to the full flow of Reiki energy at the levels below IIIa and because of lack of experience, it is unethical for you to do Reiki on the public and to charge what someone who is fully open and experienced would charge.
Other ethical practices include never treating someone who is not fully clothed. Why? Unless you are licensed massage therapist, acupuncturist, or doctor, it is illegal for you to be working on someone who is not fully clothed. Wisconsin is a "no touch" state therefore as Reiki practitioners, we cannot touch another persons naked body. If you plan on doing Reiki on the public and are not a licensed massage therapist, etc., you would be wise to become a minister as Wisconsin allows you to "touch" under the heading of "spiritual healing" if you are.
There are many people out there practicing "Reiki" who have never taken a class and have no certification. The claim they have been "self-attuned" (not possible) or that they just it naturally, so make sure when you go to someone for Reiki that their certificates are displayed out in the open where the public can see them (another requirement by the State of Wisconsin).
One last obvious ethically topic, if a Reiki practitioner comes on to you in a sexual way RUN and report them! If your client asks you to perform sexual services during a Reiki session - boot him/her out and report them to police. This occurs more often with massage therapists (I've heard many stories from my massage therapist friends about this) because prostitutes often advertise under the guise of massage therapist so the public has some misconceptions about massage therapy. Working in a spa or wellness center gives you more protection especially if you're female.
We need the public to know that Reiki is an ethical, safe, service, just like all the other healing modalities our there, so educate the public by your actions and behavior and if you know someone who is not acting in these ethical ways and doing Reiki either talk to them, or report them.