How to know if someone on Facebook is legit?

I have several people as my Facebook friends who are considered more well known. They have blue check marks next to their profile to verify it's really them. Recently, one of them posted that someone else was using his name, when it wasn't really him. Since then, he said he got the whole thing sorted out, but how do I know if it's really the right person... who he says he is?

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6 mo
Also, to add to this question, he seems to be on Facebook often, which I'd think that someone of his status, would be pretty occupied with other things. There hasn't been any other scam activity since then though.
How to know if someone on Facebook is legit?
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