I can only guess you are looking at an over the counter orthotics such as Phase IV, Alznner supports or Feathersprings. I have very little experience using these appliances and have seen patients who have bought them with all sorts of assurances from the salesperson that they would work for their problem. I can't comment on how many people are pleased with these since they probably would not be in a podiatrist's office.
If your podiatrist has recommended a custom orthotic for your problem, that might be a help, but there is no guarantee either.
So as the saying goes, "Caveat emptor" Let the buyer beware.