This includes methodology and epistemology. Much of what Einstein predicted he did so based on theory without experimentation. Sir Arthur Eddington stated, It is also a good rule not to put too much confidence in observational results until they are confirmed by theory.
Statements made by experts are a distant third.
There are exceptions of course. Everyone agreed that nicotine was addictive. AFMA frequently quotes individuals and groups who have a vested interest in animal experimentation. We also rely on logic and common sense when deciding if animal experiments help humans. The animal experimentation lobby spends millions annually to convince the public that all medical advances are directly due to animal experimentation.