Lateral Reading:
Go beyond the source. They say they are "right"or "the best". Don't take their word for it. Their bias is apt to be in their favor.
Check out the buzz: What do other sources say about the claim? Does your source have a good or bad reputation?
Be skeptical of claims. Find the original source of the claim. Find the references and see if they were correctly represented.
Use fact-checking sites: Has the claim already been investigated by a reliable fact-checker?
Reverse image search: Find out where the images come from and whether they were correctly represented.
Evaluate the original source of the claim:
Is original source prolific and popular? Then they have a reputation to risk, and would hopefully be more careful what they promote. BUT some influencers are highly biased and/or not concerned with accuracy. They may just be saying what their sponsors want to hear.
Long-standing Domain History or Institution? Check website domain with Domain Tools. How long has the website/institution been active? Being around for years suggests a reputation to risk. BUT If a website has just been created, it may only be temporary, (scam and scram).