There are probably many wonderful, kind-hearted people in your workplace. Individuals who simply want to do the best job they can for the benefit of the organization. Unfortunately, there are probably others who do no fit that description.
It's important to assess the motives of your coworkers. You can do this through interactions and observations. Pay attention to how they keep their word, how dependable they are, how they treat coworkers and how consistent they are in various situations.
This is important because most of us need people at work we can talk to when we are having a bad day. This is not daily venting but the occasional need to discuss a stressful situation either at work or at home. If you talk to a genuine, kind and honest coworker, your conversation will remain between the two of you. He or she may offer help or suggest other resources. If you pick the wrong person to have this discussion, he or she may use the information against you. It may get twisted and spread around the office. This gossiping may be done as a way for the person to appear in-the-know or to potentially hurt your career.
You may also want to consider someone's motives at work when you are selecting a coworker to ask for help or to write a recommendation. You need to know who you can trust and who you should keep at an arm's length when dealing with personal or important issues.
You can't avoid those who may take advantage of the situation but you can be more guarded in your interactions with them.