I have been on mn for ten years. In that time hundreds and hundreds of trolls have been outed and banned on here, some with truely vile vampiric tendencies. dizzymare/the fox troll/izzyruby/the one who had a tiny premature baby and then lifted someone else's picture off the internet to pass it off as her own (I can't remember her name). And there have been dozens and dozens more. And before my time there was the imfamous judge flounce, and the list goes on.
There has only been one instance of a poster being wrongly accused of being a troll in all of that time, and if mn hq were sure, then I am certain that they had good reason for knowing that she was not all she seemed, because IME hq err far more on the side of giving the benefit of the doubt than not. I wonder whether hq would perhaps clarify why they were so sure she was a troll, and whether or not there was something else in her posting/username history which meant that she had a more colourful history on here than we were aware of, but because this particular situation was real then would not be the time to divulge that.
Remember that even real liers and fantasists have real lives to, and those can involve tragedy and loss as well.
For the posters who say that troll hunting should be banned, in all the time I've been on here it's only been the calling out of suspicion on a poster which has led to mn hq actually taking more notice. Dizzymare was being reported for weeks and weeks while she drew people into her lies and deceit. Bereaved mothers who had lost a twin, people who identified with what she was going through. People who gave her their personal details, and all the while mn hq were "looking into this one." And then the twins died and she was back, and the sympathy poured out for her and there was talk of a collection. It was only when someone actually started a thread saying "look, there is a poster who is gaining a lot of sympathy here at the moment, do take care when choosing to believe everything that people say online, and take care," that multiple posters started posting that they too had suspicions and everyone knew who they were talking about. Dizzymare was then banned within hours, but she already had personal details of mn'ers, had them on fb (a totally fake account with only online connections on it, and a picture of her dead babies) started sending suicide threats to mn'ers who had themselves lost a child so felt afraid not to listen in case she really was real and did something awful. She was publically outed elsewhere months later when it transpired her pictures of dead twins were lifted from the internet. 
this was on a parenting bereavement forum iirc.
CVQ met up with mn'ers in rl, people had collections for her, she drew many, many people in, and again, people had been reporting for weeks and nothing was done.
Izzyruby met up with parents of young children, had a modelling website, people sent her pictures of their dc, and she turned out to be a suspected paedophile. Even the police were involved in that one, but unfortunately she skipped the country.
So for everyone saying "far better that ten trolls frolic freely and hopefully ignored than one genuine poster be wrongly accused," think on that one. Not everyone is cynical enough not to give money to some random username's collection, but some people are. And some people have shared experiences which mean that they feel compelled to give support. And because genuine friendships are formed over the internet and then into rl it stands to reason that the fakes will spill over into some people's rl as well.