Not being familiar with reiki, I read a few articles about it.
This one at Quack Watch pretty much sums it up:
http://www.quackwatch.com/01QuackeryRelatedTopics/reiki.html
About thirty years ago I had a neighbor who was in "alternative medicine". It was related to "supplements". She was charging people what I considered "an arm and a leg" for hair testing, the supplements themselves - because they could only get the "pure ones" from her. In addition, she provided paid "counseling" to her "patients", either in person or by telephone.
This woman totally believed in the value of this and was dismissive of "traditional medicine". She got into this through her chiropractor. To me it sounded like she a attracted people who were of the hypochondriac type of personality. But they paid.
Despite having NO medical background other than "seminars" she had paid to attend, she had a business card that had a ton of "initials" behind her name. At one point she proudly told me she had "earned her doctorate" and could now be called "Doctor". She actually began advertising her services in the local weekly newspaper as "Dr. So-and-so". Shortly thereafter, she was contacted by the state regulatory agency and had to stop advertising herself as "Doctor".
I think sometimes people become desperate for help when traditional medicine can not help them. And they are then vulnerable to "alternative" things. If these alternatives provide attention and assurance that "this will help you", that in itself may indeed help. Yes, it is likely the "placebo effect". But the placebo effect has been well studied and has been shown to be effective. It kind of boils down to how much do you want to pay to achieve the placebo effect.