It depends on what the person says and how they present it.
There are articles people write that are the type you describe - articles that offer evidence/examples from other articles. I may (if I read one of those at all) believe what the author of one of those says because it's clear he's saying what someone else with more authority has already said. I have little interest in that kind of "informative" article, though, because if I want information I'd rather get it from the authority who wrote the referenced material, rather than from someone who just regurgitates what an authority has said but who may know little about the subject or, in fact, not even know enough about it to know WHICH reference sources are solid.
As for people who write "from their own head", it's usually easy to detect the stuff that's written from someone's own ideas but has nothing behind it to back it up. That's the stuff people often write as if they're experts (often because they're too insecure to just write in the first person), but as you read it you'll see that they offer no explanation as to where any personal experience, personal reading, reasoning based on a combination of both, etc. etc. factored into the ideas/information presented.
There is such a thing as a person who knows his subject very well. Maybe it's their hobby. Maybe it's something they've done a lot of reading on. People like that, though, will usually say enough in what they've written to make it clear that they know what they're talking about. Also, if a reader were to give a quick look to some other sources that reader would see that what the person has said is not in conflict with "authorities" with "official credentials" says.
Personal experiences teach people things that "the books" don't cover. Someone who is not young is likely to have learned things that mean they know their subject. Someone who has had a lot of relationships/discussions with a lot of people may be more familiar with a subject. People who have done a lot of research for previous writing, and people who know their subject because they've done a lot of reading on it, can very much know what they're talking about. People who can explain what reasoning has gone into their own conclusions, and who have had more than just their own thoughts as input for that reasoning, can know what they're talking about.
So for me, it depends on what is said, who says it, and whether there seems t be solid "checkable" substance.