But it is not at all rare that such fly-by-night clinics grab someone's obscure result at third hand, rather randomly. They're a crap source of information, but not a disconfirmation.

Where there's an ick factor, or a safety factor, as with infecting oneself with worms to reduce allergies, the effect is perfectly real. The Mexican clinics are either are either ahead of their time or unsafe; ya just don't know which.