Wide-eyed, impressionable, easily beguiled townie casually strolling the sidewalk, preferably with his wallet open in his hands: THIS is your mark. Make eye contact and smile; position yourself in his path and affably offer a handshake. He wants to save the children.
Steel-eyed, implacable, determined man in casual business attire barreling toward you at three-quarter tilt to catch his bus: this is NOT your mark. DO NOT position yourself in his path and begin nonchalantly mumbling your shpiel. He will not be wowed by your cause.