I think the number of actual 'trolls' (folks without PTSD who are intentionally baiting others for their own jollies) is probably pretty rare
Oh there are groups of people and individuals that do this - on one forum I was on people would report back forums that they got closed down, were banned from, had heated debates in, managed to inflame most of the site. (They were regularly banned from that forum and were, in the end, the reason for the demise of that forum - still a great loss in my mind.) Those type of people get shut down pretty quickly here - the challenge for those type of people on a forum like this would be to see how long they could do low level inflaming before they got chucked out. It is a hobby for them. They would regularly boast about how they set moderators on one forum against another moderator on the same forum. They are really pretty sad individuals. I didn't realise for a long time how damaging that those people are for a forum. I thought because we knew what they did it would not effect us, and I was very wrong about that.
Then there are other individuals, for whatever reason like to go between forums and see what mischief they can inflame - and they will sit around for awhile before they go for the jugular and then they get away with a lot more because by then they have become regulars, and I don't know how you deal with those types of people. It is beyond me.
Then there are people who have emotional issues and wherever they go they fight with people - I don't know how conscious they are of these things - it would be hard to judge but you won't get through to them. They just move on. And they have patterns of behaviours that experienced moderators can spot pretty quickly from what I have heard. (My partner is a long term moderator who has to ban people regularly on a large Australian forum.)
Then there are people that have their own flame lists where everyone flames everyone else and occasionally they go to another forum, the subject of forum is not important, and cause havoc there. So that is like a co ordinated attack on a forum just to see what happens - I guess like someone poking a hive of bees with a stick.
Being a troll is a thing for some people, a hobby for other people and an identity to be proud of for some people. There are troll communities out there.
So they are out there and you can't take them personally but it is important to get them off your site ASAP.