Just last night I watched this on the local news. An American was getting ready to leave Philippines at NAIA. He was going through the scanner and immigration found a bullet in his luggage.
This is one of two major things going on at all airports. The victim was not watching his luggage properly and someone slipped in the contraband. This very well could have happened also while taking the Taxi to the airport. Always keep an eye on your luggage. This has also happened in Thailand, Singapore, and Hong Kong, but with drugs instead of ammo. You get caught with drugs in those countries it is the death penalty. Even if you do not do them hey will still find you guilty and execute you. So always handle your luggage yourself even if heavy. Keep a very close eye on them, and never carry an open bag or open style purse. The people can just drop whatever in and you are clueless they done it.
The second is the immigration scam. You go to immigration to get your departure stamp someone talks to you or you look the other way. While you are doing so they tear out a page. Then they let you board or they may even immediately arrest you. If you board the plane they call ahead and you are arrested in the next country upon landing.
Immigration employees get a bonus for every person they turn in and this is how they are making their money. This scam originated in Japan but now has found its way to the Philippines as well.
Always keep a constant eye on your passport. Do not look away until after it has been handed back to you. Then open and check it in front of the officer to make sure everything is intact.