well i will be carefull when answering this for ovious reasons, they can take you into secondary inspection anytime they want for any reason, whether driving or walking over, this is rare, they will randomly stop a certain amount of people for no reason at all, or they will stop and search people because they think you are suspicious for some reason, if you look like you work out the customs officer will usually ask you if you are bringing anything illegal over, and will 'read' your eyes so to speak, if you look really nervouse he many search you, so its a crap shoot, never know what will happen, i dont really want to say anything else for legal reasons