I'm not all that clever at identifying trolls, though I did spot one on this forum eventually (The one about a supposedly bad DIL). I always have the feeling that they might be genuine but a little odd or disturbed.
I was once on a forum, now defunct, several years ago when a very nice, normal poster, a married man with a child, suddenly turned into a troll. Many feelings were hurt, and I think it led indirectly to the demise of that forum, which was called 'Yorkshire Posts'. (Someone tried a new 'Yorkshire Posts' later but it never took off as well.) It was my first forum and I really used to enjoy it. A computer programmer at work had found it for me.
I have a couple of other Yorkshire forums now, but losing that one was sad.
Trolls - horrible!