In an era where mass media basically didn't exist, most people couldn't read, and information about how these things work could not easily spread, it might have been easier to convince people that a fake test was really what you were claiming it was. If people could google it they would instantly find out it was fake.

So guilty people were convicted, and so was anyone who knew how oil works.

Unlike now, where only innocent people are convicted and everyone knows all the science that always works, like DNA testing?

Oh, correct. I think by "work" I merely meant "here is the mechanism," not "this is why they are successful."