Spirit guides are there to help you learn life's lessons. They aren't guiding you 'toward' anything specific. It is like having a friend at your side who helps you.
I don't recall ever hearing about a spirit guide being 'untrustworthy', but I suppose it could happen(?). The spirit guides I am most familiar with are animal guides. Since all animals are pure in spirit, and think no evil thoughts, I don't believe an animal guide would be untrustworthy. Spirit guides are not usually human, they are more often animals), though some believe that they are human. The connection with a spirit guide is just that... a spiritual connection with another being in spirit form that is there to help you learn and guide you through life's difficult times. (FYI Fred...'spirit' and 'spiritual' as used here doesn't imply a connection with Christianity, etc. It is a more about the 'life force' within every living thing. Even an insect has a spirit.) Spirit guides have played an important part in many cultures (shamanic, etc.) all over the world from ancient times to present, including the Native American people.