It's by no means easy but one verifies authenticity with tools (e.g. metadata) or multiple people who do know better. In these days as we're being molded by bullshit in every step we're also getting better at spotting whether the material has been crafted to provoke a specific end/reaction in contrast to casual information.

For more ambiguous yet seemingly important stuff, it needs a thorough check for contradictions and how well it ties with other factual information.

One thing about actual knowledge is that it rarely contradicts what's already known/established and instead adds to the whole picture to provide a better/more holistic view.

In short, truth is way easier to verify while its impossible to do that with bullshit since its a thing of its own.