If some field of endeavour is genuine, you would take it as a given that the people working in it would lose their jobs in a relatively short amount of time if they veered off into complete bullshit. For example, if buildings are still being built, we can surmise that the field of structural engineering isn't a complete hoax, since if it were the buildings would collapse. This would not fit into the plans of people with the power to fire those responsible, so they would be fired.
If this is not the case, and the field can continue without such an objective test, then most likely it is all bullshit, since it is easier to bullshit people for money than do anything useful.
We could apply this test to various current industries to see whether they pass, for example space exploration, cosmology generally, evolution theory, paleontology, pre-history etc.