You missed the point of my post. Regardless of your understanding of dowsing/muscle testing/consulting the bones/tea leafs/tarot card reading/coincidence interpreting the truth is it can only give you information you already have access to but may not be consciously aware of.
Where this knowledge/belief comes from - literally where it originates (guides, spirit, cells, channeler, wherever) - is the heart of the argument and that's the part that's unprovable. You seem pretty set that cells must have the most knowledge, so maybe you should try asking your cells for information when dowsing. The bigger question is, what gives cells this information and if they're the source why didn't they pass it on to "you" already somehow? or did they? ;)
How reliable a person is at dowsing has everything to do with how capable they are at filtering all the BS that runs through our minds to leave just the truth. Then comes the question, what is the filter and where is it? Who is doing the filtering and under what guidance? And guidance from what? who? where?