There are laws that say you can’t take more than $10000 in currency out of the country without declaring it. Since the face value was only $27000, I wonder if they could tale it out $9000 face value at a time. That would be one way to avoid the IRS.
The were valuable enough that they could have slowly moved them outside of the country over many different trips over years.
Even if they didn't open their mouths and it was the dealer who outed their story, they got greedy and should have done the whole thing much slower.