You have just launched a new product. You posted about it and someone claims they have tried it and it doesn't work. You should automatically assume this person is a troll, no way anyone could have bought and used the product so quickly.
You're trying to help an unsatisfied customer. A complete stranger enters the conversation and begins to hurl insults at the MD of your organisation. You should ignore them as they are most certainly a troll.
Someone makes a complaint about your products, you ask for proof of purchase. They say they do not have it, but insist the product was bad and they need the issue looked into. This person is a troll and you should block them.
Someone with no display picture comes to your page to complain that they were sexually harassed by one of your sales agents. You should report their account and get your followers to do the same because they are a troll.
There is someone who regularly comments on your posts but they only have complaints and terrible things to say. This person is a troll.
A misinformation was posted about your brand, you correct through a press statement with facts. But someone on your page continues to maintain their stance. You should treat them as a troll.
Someone posted something terrible and untrue about your brand and you call them out on it. They apologise and claim it was just a joke. Should you consider them a troll?
You made a mistake and have apologised for it, but someone keeps dwelling on it and spams your page with triggering comments and name calling. Is that a troll?
A person complains about your brand's customer service using the words never, every and other superlatives to make their points. Your attempts at making things right only aggravates them as they continue to exaggerate the situation. This person is most definitely a troll.
A person complains about your product design and quality in poor grammar, poor punctuation and made up words. This person is likelier to be a troll than an angry customer.