There is a basic principle which applies to how much weight an eyewitness testimony carries.
Here is an explanation, from this article...
http://www.quackwatch.com/01QuackeryRelatedTopics/extraproof.html
The
weight that a person's eyewitness testimony holds is directly related to
how plausible the claim is....
before (
a priori )the claim is investigated. Or....how plausible, or outrageous the claim is, using simple common knowledge and common sense.
For example....if someone says they saw a T-Rex walking through the woods, then their testimony holds NO weight, because we know,
before (a priori) investigating the matter, that that is an impossibility.
If that same person says they saw someone steal a car, their testimony can hold a good deal of weight, because we know
...a priori...that claim is a very plausible one.
The tricky thing to figure out....and agree on....is the "
a priori plausibility" of claims which are
in-between those two extreme examples.
Like, the "a priori plausibility" of "Bigfoot's existence".
Is it really so "outlandish" a thing, to think....
before investigating...that such a creature
could exist, somewhere on this planet?
It certainly is more outlandish to think that it could live in a suburb of Chicago,
than out in the wilderness of the Pacific Northwest.
It's an important part of 'weighing' a person's testimony, because the extent to which it's either plausible, or implausible, is a major determining factor in applying a certain weight to someone's claim to have seen a Bigfoot.
We know that upright-walking primates
do exist...

...and we know that Giganto
did exist, and it fits the basic description of Bigfoot, with the possible exception (and the
only one, btw.) of the 'upright posture'.
I, personally, don't see any reason why Bigfoot's existence should be considered an "outrageous", or "highly implausible" claim...in certain parts of N. America.