First of all it's FinCEN. Secondly, there are about 12,000 financial institutions in the US alone, some of the large banks have that many, or more, branches. The number of SARs completed by financial institutions that involve actual criminal activity and money laundering keep FinCEN busy enough.
Lastly, these people funding these payments aren't stupid people. They are well aware of the thresholds of BSA/ AML reporting and will adjust their activities accordingly.
Lastly, these people funding these payments aren't stupid people. They are well aware of the thresholds of BSA/ AML reporting and will adjust their activities accordingly.