Take the adjective coy for a person who pretends to be shy but really isn't, or someone who could give a definite answer but won't. Coy behavior can be playful or just plain annoying.
Originally meaning "quiet and shy," today someone who is coy pretends to be shy in a playful manner — often as a form of flirting. If a politician is coy about something, he or she only gives vague statements on an issue for fear of committing to a position or angering his or her constituency. Common to both of these senses is the fact that a person uses coyness to subtly manipulate his or her audience.