Like everything else -- what evidence do they present and what credentials do they posses that makes them a valuable interpreter of such evidence.
"If it's on the internet, it's true" is a real thing.
The following isnt just for youtubers, its for all information.
As individuals, we can ensure they present evidence. If we're going to attempt something drastic off this evidence, ie, claim Scottish Lordship, we should validate the evidence ourselves or ask a credentialed validator. Ie, a Scottish lawyer.
* Did they present evidence? * If yes, do they posses credentials that make them a meaningful evaluator? * If yes, do other meaningful evaluators agree?
It's not dissimilar to the scientific method.