[The thread is kinda dead..
Do you guys look at how the girls look like before be friend with them?]
Yes but normally I simply use looks to determine what I think their normal personality is once we get to talking I use that as my point of reference for whether or not I like them or not as friends or otherwise. If I look at a girl who dresses up in the latest fashions and smiles alot I prepare myself for a time of just listening while they talk. Dresses in leather with multiple piercings I will not actively go out of my way to talk to them etc. But actually talking to them for awhile is how I ultimately judge a person.
[If a girl confessed that he likes you how can she know that the boy feels the same way too?]
What Shadow_Strider said essentially covers it but personally I'll go out of my way to talk to and be with the person, use a real smile and wave when I see her, and listen intently and quietly when she speaks only interrupting a few times when I feel it is needed or expected. If its someone I like I don't act nervous in their presence but if its someone who has confessed and I don't I get overly nervous around them and try to take paths where I won't run into them as often but I will still try to make them happy till either they lose interest or I can find someway to let them down easy.....hard as that is.