Don't let others manipulate YOU
If you detect that someone is deliberately attempting to take advantage of you, do not remain tight-lipped -- stand up for yourself!
Approach the individual in a tactful manner and ask when he or she would be available to have a conversation in private.
Hopefully, doing so will defuse the situation. If you find that the relationship is beyond repair, make it clear that you won't allow him or her to disrespect you.
A good person doesn't try step over his or her loved ones just to get ahead. That bespeaks utter selfishness and a lack of a moral compass.
Anyone who does this deserves no place in your life unless they can offer a convincing apology, vowing to never betray you again. After all, it's hard to restore trust after one feels they've been stabbed in the back.
Again, if you sense that someone might be trying to take advantage of you, don't stand idly by. I can assure you that once they see you don't let anyone play you for a fool, they will never dare to do it again.