Many commonly held beliefs form years gone by have been proven to be wrong: "the Earth's flat", "the stars rotate around the earth", "you can catch cholera from bad air". So should we put our faith in experts? Well, the experts of their day all believed in the statements I've just mentioned, so that doesn't help. And the majority of common folk probably believed them too.
So who can we trust?
To my mind the only solution is to base decisions on the best possible information - the best evidence. And to be willing to adapt whenever a decision is proven to be wrong.