Suppose I did prove that I am such a forest ranger. Would my story about putting on a gorilla suit make you more or less confident about my claim to have seen bigfoot?

That would highly depend on how many other expert forest rangers corroborate your account, and how much sensor data accompanies your claim.

I also think the focus should be on witnessing something. Saying it’s definitely Bigfoot is an interpretation of what you saw. Maybe you saw the same phenomena other people saw and believed to be Bigfoot. Maybe what you saw has explanations that aren’t currently accessible.