How to Distinguish Between Useful Criticism and Trolling

How do you differentiate between a true fan and some one who doesn't get the joke? There is a key distinction bet feedback, advice, criticism and trolling. When a non believer shows up with criticism or trolling, it's not helpful to you if someone who doesn't like musical theatre comes along tells you that your broadway musical is no good. We've got to have the guts and the generosity to see people who are like the people we are seeking to serve.