What is it about “shopping while black” that’s so hard for some store employees to understand? In the past week, two troubling incidents involving African-Americans at local retail outlets should prompt employers to offer a refresher course on customer relations. It should be made crystal clear that it’s not just morally wrong but catastrophic for business when people assume that skin color equates with potential criminality.

The moral argument should be compelling enough. It is simply racist for anyone to assume that black customers automatically merit extra scrutiny.

But moral arguments don’t always prevail. That’s where the business argument comes in.

Whenever American consumers, whatever their race, see wrong-headed business practices, the potential for disaster is enormous. Consider the backflips that Starbucks’ managers now must perform to reassure customers that the company won’t tolerate racial bias.

Starbucks plans to close more than 8,000 stores on May 29 so its 175,000 employees can receive racial-bias education.

All this because one employee in Philadelphia called police when two black men failed to comply when asked to make a purchase or leave. They had simply been waiting for a third person to arrive for a business meeting, presumably over coffee.

The Starbucks nightmare apparently didn’t resonate with employees at Nordstrom Rack in Brentwood and at a local Schnucks supermarket, where black customers were humiliated for no apparent reason other than their skin color.

At Nordstrom, two high school seniors and a 19-year-old college freshman were shopping last week when an employee began monitoring them and later called police, accusing them of shoplifting. The officers, to their credit, listened to the youths’ version and determined that the accusation was bogus.

Nordstrom Rack’s President Geevy Thomas flew to St. Louis and met Tuesday with the young men and their families to personally apologize.

At the Concord Village Schnucks, a Belleville man and his girlfriend tried to purchase a $1,100 money order to pay rent.

An employee refused to let the man, Kellen Hill, purchase a money order using a debit card and his Florida-issued driver’s license. His girlfriend arrived with cash in hand to pay it. The employee still refused, even while insisting, “We’re not racial profiling.” Most of the encounter was recorded on video, including Hill’s repeated warnings to the employee that he was going to lose his job. The employee wouldn’t budge. Sure enough, he was fired – and rightly so.

Schnucks chief executive Todd Schnuck apologized, saying he was “incredibly disappointed in the poor judgment that was used in handling this incident.”

When top executives have to scramble to avert disaster, it’s a clear indication that staffers far down the line didn’t get the right message: Racial bias, implicit or explicit, is an offense worthy of a swift and unsympathetic boot out the door.