So up to date in Hamlet, Hamlet meets his fathers ghost and is told how he was really killed. After, Hamlet doesnt trust his step father nor his mother. Speaking of trust, Laerities and Hamlet are spied on, but Hamlet realises so.
Hamlet demonstrates his desire to trust and reluctance to trust before he explains what he and the ghost of his father talked about. We know trust is an issue with Hamlet because he is so reluctant before he tells his friends the truth and because his mom broke his trust when she got married to his father's brother. Hamlet's father's ghost has to force Hamlet just he did with his friends to not tell any one the secret that has been told. It's obvious Polonius doesn't trust his son because he sends a spy to his son's school.