Your bank is not required to serve as the de facto regulator of the NBFI. Furthermore, your bank should not be held responsible for the NBFI's lack of compliance with the BSA and other applicable federal and state laws and regulations.
That said there is no way to be 100% certain that the cash being deposited in Mexico is legitimate. If I was forced too, I would insist upon knowing your customer's customer in this situation. I would want some type of written agreement from the NBFI stating they will not conduct business with CDC's. If not, what's to stop the NBFI from opening accounts from CDC's and thus allowing those accounts to become nested accounts?
In terms of justification, how about:
1. Their current bank threw them out
2. The Wachovia CMP
3. Go to CNN and search Mexico and Drugs
4. Given the amount of work your department will have to do, will this relationship not just be profitable, but profitable enough to risk your bank’s reputation?
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"100 victories in 100 battles isnt the most skillful. Subduing the other's military w/o battle is the most skillful." Sun-Tzu