Sincerity plays an important role in trust. Do not just be nice for the sake of getting something of others. It is true that you need to be polite when asking others of help, but don't just seek that person only when you need help. Be sure to thank that person as well and not take that person for granted. However, sometimes being polite doesn't justify the satisfaction of others as well as they may think that you're being unsincere..... that's how complicated relationships are. The world is imperfect..... yet at the same time you can say that it is because it is imperfect that it is beautiful and interesting.