It still remains aproblem to know what sources count as reliable. Reference books carry errors - we all thought Encyclopedia Britannica was authoritative until Harvey Einbinder published The Myth of the Britannica(1964), showing how full of errors that great work was.
The latest Brewer's Dictionary has errors.
The US academics Boller and George, in "They Never Said It" uncover many misquotes, fake quotes and misattributions that even a work like the Oxford Dictionary of Quotations continues to repeat.
I have a shelf of books of Popular Fallacies, fallacies which are constantly repeated. For example,it's not the case, according to Professor Tom Burnam (The Dictionary of Misinformation, the the Declaration of Independence was signed on 4th of July (Hm - 4th of July - that'd be 4/7 then)   
Many reference compilers copy errors from other reference books.
World Almanac was still printing the idea as a fact that King John signed Magna Carta.
It can take time to see how different media skew things and why.
Melvyn Barg, in his In Our Time series on Radio 4, managed to do 45 minutes on te history of astronomy, and the same period on Isaac Newton, without, in that 90 minutes, mentioning astrology once. So one way to check on a source is to see what it leaves out, and those who know less than their source can be mislead out of ignorance.

My point is not that nothing is to be trusted - that would be ridiculous - but that getting the facts requires constant vigilance,and holding