I managed to do a whole post on medical/pharma cranks without mentioning one of the biggest factors of all. As many people pointed out in the comments, look out for any therapy that makes a big point of being "all-natural".
There are several interesting mental attitudes behind the success of that marketing ploy. One of them is the appeal to primitivism. I'm reading Jacques Barzun's From Dawn to Decadence, and that's one of the persistent philosophical currents he identified in Western culture. Back to the basics! Shed the corrupting influences of modern life! In medical terms, this shows up as a constellation of beliefs: that people were truly healthier back in the good old days, that, correspondingly, there's something about modern civilization that's making us all sick, and that remedies for such ills are not to be found not among the fruits of that industrial civilization. Why would they? It's like a drunk reaching for an eye-opener to cure a hangover, right? No, you want to go back to the simple, natural remedies, because only those can cancel out what's been done to you.
I should mention up front that these beliefs are not totally insane. One of the things that I took away from an earlier book that I recommended here, A Farewell to Alms, is that life expectancies and general human health actually took a bit of a dive as cities began to grow in importance. Dietary and sanitary standards were lower for the mass of people in London, say, than they were for the farmers in the countryside, and it showed. And even today, some of the less-developed countries are in even worse shape than they were before the modern world ran into them.
But those aren't the customers for pricey natural remedy come-ons, are they? No, those go to well-off first-worlders with disposable income and high life expectancies. Industrial and urban civilization, although it got off to a pretty dirty start, has in fact led to a great upsurge in human health and productivity. And that's given people the time and wherewithal to respond to ads on their large flat-screen TVs or their satellite radios, and to pay money for shaken vials of distilled water or ground-up plants shipped from the other side of the planet.
Speaking of those ground-up plants reminds me of one more mental attitude. Among people who are big herbal medicine believers, there can be a sort of teleology, a view of the world as if it were more rationally constructed than I think it is. I've seen people asking questions like "I have Condition Y, what's the herb for that?" This every-disease-has-a-plant-for-it view is quite odd to me, because I don't see any reason why it should possibly be true. Plants make medicinally active substances for reasons of their own, and they only overlap with our needs once in a while. And for that matter, most of the really active compounds found in nature are things that will mess you up, rather than help you, just like most of the really active compounds made by humans. There are simply more ways for our biochemistries to be interfered with than for them to be improved.