If you noticed, nxt time when you are waiting at the carosol to
pick up your baggage, look towards the extreme right - you will see
a wall lined with mirror. I think that is a one-way mirror,
already, they monitor the ppl from there and even before you pick
up that piece of luggage of yours, they already mark you to
check.
They observe your body language. Cos if you are smuggling
something, chances are, your body langugage will betray you. On top
of that, they act on tip-offs.
I think as long as you are behaving normally, chances are, you
won't be stopped. But if you are scared, then don't smuggle things
loh, be good boys.