From my own experience, I think it's important to judge people by their actions, not by their words alone. For example, if someone says, "I'm here in school to study, I didn't come to college to party," but later on you overhear that person talking to someone else about some bar they're all going to, their actions are clearly inconsistent with their words. Also, some people tend to change their behavior and personality depending on the group of people they are surrounded by. They may claim to hold a certain opinion about someone or something while around one group of friends, yet state a totally different opinion about that same topic when they are around a different group of people. These kinds of people are manipulative, in a way, trying to project the persona that they think other people want to see. I find that it is helpful to think back on people I have met in the past who I have been close to, and remember who I got along with and who I didn't. When I meet someone whose behavior and interactions with others strongly remind me of other people who I found to be untrustworthy, I usually avoid them, and that usually turns out to be the right thing to do.