Imagine that Bob claims to have discovered the great long-lost youth rejuvenation potion of the Mayan civilization. Bob tells you that 100% of all people that have tried the potion say that it works! Tom and Jane have tried it, and they say it works too! Bob isn't going to tell you what the ingredients are because it's an ancient secret. Everyone who's tried it will attest to you that its real, but we obviously can't prove it to you over the internet. If you want to know more, you can come and pay X amount of dollars to see what the big deal is...
Just to refine your example, it may be the case (regardless of its effectiveness) that the potion is not of Mayan origin. The question of the potion's provenance is completely unrelated to its efficiency. For example, Jane may say that she feels younger but the fact that the potion doesn't have the typical Mayan taste of maize but rather tastes like Mexican salsa, make her wonder where the recipe actually came from.
One may argue that if the potion works (you just have to feel it!), the provenance makes no difference. That is really a matter of personal opinion, so going back to martial arts, I choose to practice Aikido and if it was to be statistically demonstrated that in most engagements a Karateka beats an Akidoka, I think I would still opt for Aikido.
Regarding the 100%, I have been to one of Dan's seminar and while I saw some interesting things, it is clear that an immense ammount of work and determination has to be invested, preferably in a supportive environment,
to reach the point that is equivalent to "ingesting the potion". This combined with strong personal conviction that the potion is not of Mayan origin contributed to my decision to let it go.
About the money, as I said before, anyone is entitled to charge whatever they feel like for their time and knowledge.