The inconsistency of bag screening in Bali has just been mentioned. Could I suggest that it could be a matter of language that means that some people have their bags checked while others do not? Normally when my bag is checked in Indonesia, the satpam (security guard) does not even speak to me. When I have gone to KFC (god forbid) in the back end of Jakarta for their air con and a coke, all the counter staff run into the kitchen and then work out who will come back and try to take my order. Languagewise they are high and dry. It is no one person's fault - it is just the way of the system.
Remembering that most people in Indonesia can't communicate in English, it could be that security guards, often with no more than junior high school education, who are in the front line of protecting people, but yet dont even have the basics of "Excuse me sir, I need to inspect your bag. Could you open your bag please"? The whole thing will always be hit and miss while there is a linguistic brick wall between person A and person B.
I doubt there are many Security guards at Melbourne Airport for example that could punch out that request in Spanish or Hindi or Mandarin. I could not. I am dead certain that the satpam has been ordered to examine all bags, but in practice, without having English skills or German or Japanese and so on, it is a random system at best. Cheers. Thomas