and they were carrying $16,000 in cash?
http://customsandinternationaltradelaw.com/2013/12/13/intern...
The point is that the totality of their actions are not supporting their story very well.
On my daily routine I see plenty of people who magically drive luxury cars even with jobs that, on paper. would require probably ~50 years of more to accumulate the required amount of money to buy such a luxury.
No problem if you disclose and explain what it’s for, and in some cases can explain where it came from.
This is a basic money laundering protection policy almost every country I’ve gone through has similar.