Applied Kinesiology, when done correctly (phrased in the right context and no positionality/biases), produces 100% repeatably verifiable results in double-blind test studies. It's not a local phenomenon (i.e. the body responding to the stimuli), it's a universal phenomenon -- the answer is coming out of Universal Consciousness itself, as expressed through the body's acupuncture system. However, due to ego distortions, incorrect technique, or chi imbalances in the body, it may not be as accurate when doing it by yourself, or with others.
See if you can get Dr. Hawkins' "Power vs. Force", it explains a lot of this in the book. "Truth vs. Falsehood" contains many of these calibrations done by Dr. Hawkins himself and verified by others, which pretty much makes it 100% correct (20 years of exp. using kinesiology, and no ego to distort anything