1) Trolls virtually always appear very suddenly, like a big, painful, pus-filled pimple. Typically they emerge (like a daemon from Hell) as a provocative comment on your thread, and it's the first time you've ever heard of this individual. They are not to be confused with spammers, who represent a related (but largely orthogonal) class of social networking vermin.
2) Your first impressions regarding whether or not a comment has been generated by a troll will almost always be accurate. That is, if your gut reaction to a comment is that you're being trolled, you will likely be very accurate in that appraisal. Outrageous and/or highly provocative statements designed to trigger emotional responses are their hallmark. Occasionally you'll come up against a troll who takes a slower approach and attempts to draw you into a what appears to be a reasonable argument, but this is quite rare since most trolls aim to do maximal damage to as many threads as they can, as quickly as possible.
3) "Professional" trolls ("pro-trolls") usually prowl public G+ postings explicitly looking to spread disinformation and propaganda -- or even "simply" to disrupt threads -- in furtherance of specific goals, often politically or racially oriented. Some of these trolls work in organized packs, sometimes with serious funding behind them as systematic social networking disruption agents. Despite the tone of their postings, professional trolls are usually not actually nuts or idiots, and are very goal-oriented.
4) Freelance ("opportunistic") trolls usually work alone, and unlike "professional" trolls, they often *are* nuts and/or idiots. Their comments will be at least as provocative as those of pro-trolls, but may tend toward higher levels of wackiness that expose their lack of true goal orientation.
5) Both in the case of freelance and pro-trolls, a quick examination of their G+ profiles and postings is usually extremely useful to verify their status prior to blocking. Dead giveaways of their "trollness" include either a stream of nearly identical postings, a variety of postings that tend to all be concentrated within the "troll zone" of inanities, or very few (even zero) postings of their own at all, the latter suggesting that they rapidly create new accounts as their previous ones become heavily blocked.
6) Without exception, trolls should be *immediately* blocked when detected. Unless threats or the like are involved, it is usually not necessary nor appropriate to also report their profiles. I recommend blocking troll profiles quickly and mercilessly, and not even bothering to flag the individual comments, again unless threats or other illicit behavior are involved. In cases of threats, etc., you may want to flag the individual comments, then block and report the troll's account.
7) It is usually good practice to delete a troll's comments from your thread, to avoid later legitimate commenters being drawn into the maelstrom. You may also wish to strongly consider deleting any responses to the troll that fed the beast, especially since leaving those other comments in place after deleting the troll's comments tends to leave a disjoint comment flow that can be difficult for later readers to understand.
8) Whenever you block/report a troll, and/or delete their own comments and possibly other related comments, consider adding *your own* comment on the thread explaining what you have done. A note as simple as "Troll blocked and associated comments deleted" will usually be adequate.
9) Most importantly, show trolls absolutely no mercy. Block them immediately. Your threads are your responsibility, and you are under no obligation to host comments designed as weapons of destruction. Individual trolls rarely return -- they usually move on quickly to greener pastures. Their entire purpose is disruption through asymmetric attacks. You should feel absolutely no hesitation at blocking them, and no compunction for having done so. The saying *Do Not Feed The Trolls* (DNFTT) holds true. Do not engage them in conversation. Do not argue with them -- you might as well be arguing with a roll of toilet paper. Block them now. Report them if necessary. Clean up any damage they've done to your threads by removing their comments and related comments that could waste the time of other readers.
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The wonders of social networking can only stay wonderful if we take individual responsibility to moderate, manage, and curate our threads, on Google+ or anywhere else.
This means taking our roles as thread creators very seriously, and not enduring the presence of trolls on our threads at any time -- not for any reason. No excuses. No exceptions.
Together we can help make Google+ as troll-free as possible. Human nature being what it is, we will never be entirely successful at this effort. But we can certainly give it the ol' college try.