Snake oil is a remedy that is sold for a condition that does not work any better than a placebo. How many remedies that are ‘sold’ for plantar fasciitis don’t work better than a placebo? There is probably a lot.
The biggest problem with plantar fasciitis is that the natural history of it is to generally get better on its own. Just look at the placebo groups in the clinical trials to see how many do get better on their own without treatment. The only reason to treat it is that is hurts and can take a while to get better on its own. The problem with any treatment given, the question is that did the treatment work or was the plantar fasciitis just get better on its own at the same time as the treatment was started. that is why we need to rely on good randomized prospective clinical trial to sort out the treatments that don’t work better than a placebo vs those that do work better than a placebo.