There's a real nugget of wisdom in listening to angry customers. So many customers will say something nice to not offend.

When someones passionate and says you've got it wrong and here's where - you should pay careful attention. Perhaps 20% are trolls you can safely ignore but the rest will tell you what people were thinking but were too polite to say.

So many fellow entrepreneurs tell me breathlessly about this person or other who liked their startup. I always ask did anyone say they didn't like it? Usually they say sure but I just ignored them - big mistake.