The world is filled with sinister, scheming people. Everybody sins. Everybody is greedy. There is no such thing as someone born pure and dying pure. Unless you are talking about some divine being manifested in a human's body. Even though there are all these sinister people in the world, we still find friends. We, the sinister, scheming, greedy people, befriend each other. We still make friends although we know we are evil in so many ways, though we know we have sinned so much. This is because; within us all is a beauty. This beauty is love.
All of us have friends, some are really good ones, some are just out to use you. How would you know?
Just look at everybody. We all have a motive when we make friends with somebody. We all have intentions, be it good, bad or just looking for a friend (totally harmless). People don't just make friends for the sake of making them. Some of us make friends so that we can benefit from them. Now 'benefit' might be referring to either learning morals or values from them, or just plainly leeching off of them.
Some people make friends because they are looking for a friend, and as I said, it is totally harmless. Some people need to be opened up to though, someone needs to initiate the friendship, or there will be none.
So, how do you know who your friends are?
Simple, just don't bother so much, just don't think so much and make as many friends as you want. It makes life a whole lot easier if you just let life go as it is... If you want people to be friends with you, just try to make friends with them. You don't have to find out who is right or wrong, the truth will slowly come out... It might be all the more painful for you then, but you have to bear with it - after all, you aren't God, who knows all.