I have an friend who was born & raised in the US, is over 70 years old who went to the Bahamas and got lucky in a Casino to the tune of about $25 k. He flew back to the US with 250 $100 bills in a money belt around his waste and luckily did not get caught by Customs. When I told him about the $10k limit he was shocked. He had no idea what the law was.
The guy is no dummy and he is definitely not poor. He owned his own construction business all of his life and has tons of rental properties in several states, but he was never an "international traveler" and never had any reason to be aware of such a law.
But, he could read the customs form they gave him on the plane, and, it is *CLEARLY* stated on it you must declare cash or securities carried on your person in excess of 10K. It's not like you learn this in lawschool. It's says so on the damn form.
Have you ever heard any of the stories of skinny wealthy jews (I am a poor Jew) who came out of South Africa wearing heavy coats and if you put them on the scales they weighed 400 pounds.
Take that coat off and gold dangling and hanging everywhere. In SA you can only take a certain amount when you immigrate so smuugling gold and diamonds is massive.