Yeah, very common trait for people to claim dowsing ability but can't do any better than "random chance".
I used to attend these dowsing gatherings. There were some people there who could use the rods but not that many.
It requires much practice and most people never learn it. It's available to everyone but almost no one is willing to put in the necessary time and effort.
The frequency generator machines do work. Just something as simple as a cheap DDS signal generator, a couple ground probes, and two pieces of bent welding rod. Learn that first before spending thousands$$$. I tell people to practice deep breathing techniques like the yoga breath or some other basic form of meditation to learn to quiet the mind. A GSR (galvanic skin response) can really help with the biofeedback. Usually they say to practice the techniques for eight weeks before expecting any results. So you can practice both during that time.
After you learn then maybe you can better evaluate any of those obscenely expensive rods.
Don't know if you have seen this, but this the Contraption. Better to view it on youtube because I put a few comments there below the video.
https://www.youtube.com/watch?v=O0FI...ature=youtu.be