How do you know that someone you like likes you back?

Well, depending on the person, they may do some of the following.

-stare at you until you catch them, then continue staring when they think you've stopped looking at them.

-constantly bump into you or do something to give them an excuse to touch or be close to you. They may complement on something like a necklace, then go to feel it.

-ask you for things they may or may not need constantly, and not ask any one else.

-tease you.

-they may be a little territorial over you, or overprotective.

-they seem to talk/joke/mess with you more than anyone else.