Even though "news" is by definition simply a reporting of the facts, you just can't believe everything you read or hear. Wise words to live by. So is the adage that 'if it seems too good to be true, it probably is.' Both are good to remember when dealing with the news.
People make mistakes. Journalists make mistakes. People mislead other people. People (i.e., sources) mislead journalists. And then there's the "telephone game" phenomenon that can produce a very different ending story than the original one, as people filter or forget information they pass along to others. Again, it can be either unintentional or intentional. Regardless, no one should believe everything that they read or hear in the news.
So how do we know if a news story can be believed or not? The only real way to know would be to do your own research. And I suspect that this is the real goal of a good "news" story; to get people to think and question, prompting them to find out more on their own. To search for the truth. True news outlets do not necessarily try to convince you one way or another about a piece of news they report but rather try to generate enough interest so that you - the people - become curious and follow up.
Before the internet, you would likely have gone to the library where you could access any number of different sources - books, newspapers, magazines, microfiche (does anyone know what that is anymore?), and even the librarian. In today's world, you can just Google it. But the ease with which we can now find information does nothing to help us determine what information we can trust.
In fact, we know there is a lot of misinformation floating through cyberspace, just waiting to be found and consumed. Just ask the Russians. But they are not the only ones engaged in internet misinformation campaigns. Take a look at the bias ratings of media outlets from AllSides, whose mission is to "free people from filter bubbles so they can better understand the world and each other." I haven't even heard of many of these sources, nor do I necessarily agree in all cases with their ratings. But it provides a good place to start in terms of trying to get an unbiased - or at least less biased - perspective on the news.