DealBook: To Purge Some of Social Media’s Ugliness, an Unlikely Lesson From Wall St.

A simple rule that bolsters the banking system — “know your customer” — could help combat fake news and hate speech online if companies like Facebook and Twitter embraced it.

With Interest: The Week in Business: Mexican Border Drama, and Trump Butts Heads With the Fed

Plus, the latest news on Boeing’s plane troubles, and more Brexit angst.