Assuming already poignantly corrupt authorities have any reasons to police themselves, they also have a billion ways to stall, cover and act innocent
"Oh noes, we've been so overwhelmed, I swear I was just about to approve this, woe is me",
and it will probably be true (The first part at least), they just take advantage of it
Also there's no clear chain of custody for stuff or incentive to have it, "Lost somewhere in customs" is about as precise as you usually get at the best of times
In terms of 3rd world corruption, this one is easy to solve. But the fact that it isn't solved is what makes it a 3rd world country. You put pressure on the low level corruption so it moves higher up the chain. In well functioning capitalized countries, the corruption happens at the corporate banking level. You can't have a well functioning economy without the smooth movement of goods and services.
Also there's no clear chain of custody for stuff or incentive to have it, "Lost somewhere in customs" is about as precise as you usually get at the best of times