The upshot was that although Internet trolls are a small minority of overall Internet participants, those respondents to the team's surveys who self-identified as enjoying disrupting online communities also scored highly in the "Dark Tetrad" of personality traits, the researchers found.

"[T]rolling correlated positively with sadism, psychopathy, and Machiavellianism, using both enjoyment ratings and identity scores," they wrote. Which is to say, the respondents who identified themselves as trolls also indicated that they enjoy making others suffer, lack remorse and empathy, and have no problem with manipulating and lying to people to achieve their ends.

The fourth trait of the Dark Tetrad is narcissism, which was also displayed in buckets by respondents who cited "trolling" as their favorite activity when commenting online.

Sniper trolling is *always* justified, but not related to any of those negative traits.  It's purely about injustice.   :-)

Sniper trolling is targeted at people who deserve it.

Whereas people who troll for fun are more like the description in Janill's article. 

I don't know sniper trolling, but I'm guessing it's gaming vigilantes exerting some justice on bullies/trolls within a game?