Robert G. Newton in his book "The Truth of Science" (Harvard University Press, Cambridge, Massachusetts, 1997) talks about the Criterion of Coherence.
Newton said that "the most important criterion for ascertaining the truth of a statement is its coherence with a network of assertions that are also regard as true."
In regard to the often made accusation of proponents of unorthodox ideas ( parapsychology,etc) that scientists are inappropriately dismissive of their ideas and are elitists or closed minded he says:
"Researchers justifiably refuse to listen to these claims,to examine them or refute them in detail,because they are incoherent with the rest of our scientific knowledge."
Reiki and distant healing and homeopathy-to name a few-fall outside the boundaries of the coherent web of scientific learning while the possibility that a given herb or root might have some active pharmacological effect and be beneficial does not.In regard to the later there are numerous examples while the former violate too many well accepted and established and coherent scientific principles to seriously expend research time, money and brain power to bother to refute them. Manipulation of an undetectable energy force that is capable of healing any and all diseases,the mastery of which has to be taught by a master should not have to be investigated by a dubious controlled clinical trial.So the difference between testing saw palmetto and Reiki is the difference between testing something that is considered possible in the wide web of scientific knowledge and testing something that is just absurd.