There is a world of difference between a guy who is shy, and one who is simply not interested in you. Many common-sense clues are available if you hone up on your observation skills and take note. What type of personality does your guy have? Does he appear shy and laid back every time you have opportunity to watch him? Even a guy who is shy will send signals that he's interested in you, and the signals aren't as hard to decode as you might think.
A shy guy who is interested will often be caught stealing a peek at you. He may turn away quickly if he catches your eye. When a person isn't interested, they don't go out of their way to sneak glimpses of you. A shy guy who is interested might also make sure that he's in close proximity to you even if he's afraid to step out on that limb and make a move. Does he seem to show up at the same places that you do? Does he place himself in situations where you're likely to be in attendance? This is a surefire signal that a guy is interested in you.
A shy guy that is interested will also throw feelers out into the vast sea of hearsay. Has he asked his friends and your friends about you? Have you heard word of mouth that this guy has been inquiring about you? This is a major clue that indicates interest, whether your guy is shy or not. It's his way of letting you know that he's interested, and his shy-guy way of hoping you make the first move.
A guy that isn't interested definitely won't be concerned about placing himself in close proximity to you. He certainly won't make a point or even be slightly concerned about looking at you. A savvy woman can sense aloofness and disinterest if she pays careful attention. Even a guy who is shy, but likes to play coy, will still try to look at you simply because it's human nature to look at our paramour. A guy that likes you will be keeping careful tabs on you even if he doesn't have the chutzpah to make his move!