I've only had to ban two members of my community so far, they registered to do nothing more than post a spam advertisement to a cryptocurrency site. Those are the types I ban immediately, the ones that come to my board to do nothing but spam. Trolling can, at times, be harder to distinguish for some of the aforementioned reasons, but you'll eventually know if they are trolling based on how your members react to them.
If an active member is spamming or trolling I would probably warn them first and if they continued I would probably go to a much drastic measure such as banning or suspending.