Hi There,
I am German and live in the UK. I have realised quite a few people put up sweat lodges against money here (same in Germany these days). Moreovere, here in the UK less and less people claim a "tracable" Native American tradition. The trend seems to be rather to cloak the whole thing in Celtic/Germanic mythology, or sometimes in very cloudy Native terms, such as e.g. "the maya calendar".
I personally think these people are wrong in charging money, but also and more importantly, I feel they are missing the point.
However, I have the impression the "spiritual workshop" crowd (I think they dislike the term New Age here) are exactly after what is offered on these workshops. That is, a lot of colorful images, a lot of stress on the possibility and power of personal transformation, a little bit of low threshold group therapy exercises, very little investment or commitment other than the workshop fee, and quite a bit of gratification of one's own narcicism.
Telling them off will have little effect, especially if no reference is made to Native American traditions. I guess this is freedom of religion. Or of group therapy, if you want.