Apply OFAC blacklisting extremely overly aggressively ... suffer an insignificant number of pissed off customers (who probably don't even leave you because everyone else is also awful).
Apply it as non-agressively as you think the law permits, or somewhat more than that... and find out that you're facing criminal charges because a prosecutor thinks the line was slightly different where you thought it was.
The situation is made more complicated in part because if prosecution isn't aggressive there are enormous sums of money ready to flow through whatever loophole exists and plenty of _bankers_ happy to help guide clients in blacklisted places through them. [ https://www.nytimes.com/2019/04/09/business/standard-charter... ]