How do you if someone is taking advantage of you?

An email I shared to several young people, especially girls, on 29 January 2010. I thought this is still very good to take as warning.

You know if someone is taking advantage of you when you do not feel safe with them. Anytime there is a question about someone's motives, that is an indication that you cannot trust that individual.  

People who care about you wont try to take advantage of you and you will feel secure around them. 

I'm going to assume the person you're asking about is male (since "player" usually refers to a guy). Here are some clues:

• He takes cell phone calls out of your earshot. ("This is a business call--I have to take this privately.")
• He checks his phone's caller ID and refuses to answer certain calls, then won't answer questions about who called, or tells you it was a telemarketer or a number he didn't recognize.
• That thing about always "working late" or attending work functions that seems like a cliche? It's usually not.
• He's more attentive and/or sexual than usual. On the surface this seems like a good thing, but it can be suspect because he could be using it to counter his guilt or keep you from getting suspicious.
• Mood swings! Does he become very chipper when he's got someplace to go? Is he moody when he's "trapped" at home with you for long periods of time?
• If he's playing you with someone you both know, keep an eye out for him talking about that person more often than usual, or getting defensive should you say something negative about her.
• His taste in music suddenly seems to change, or he's watching new TV shows that you would've never expected him to watch.
• He's sexual, but not necessarily affectionate. He may stop saying "I love you."
• He's more protective of his privacy than usual. He "guards" his cell phone and computer.
• There are unexplained charges to any of your joint accounts.
• He gets angry and defensive if you bring up anything that seems suspicious. He may even argue and storm out of the house. Guess where he's going?
• Your intuition just plain tells you that something's not right. Trust your instincts, because you're probably on to something.

(Source: http://wiki.answers.com/Q/How_do_you_know_if_someone_is_taking_advantage_of_you)