It required scanning multiple debate locations, looking for all posts by the same two people in other, isolated places, which I had only done by accident. But I have seen it happen more than once. The other sorts of things that give trolls away are equally obscure and not immediately obvious, but if you keep your nose sharp you might catch one. Naturally, you need not worry about hurting them. But once you have caught a troll, you can cease taking them seriously, so simply ignore them.
Some people are indeed scared.
Their fear gets translated in many ways. There are other manifestations, as you may no doubt notice. It is much easier to achieve. The objective must always be to get deeper and deeper. But by remaining polite and inquisitive and concerned, you will make yourself less of a threat, even though your views will remain frightening to them for one reason or another.