When I was a teenager I serviced my father’s car at a local garage where the owner favored the grimy walls with pin-up posters of exotic beauties. Beside them, I remember, he also had a red-lettered sign that declared: “In God We Trust, All Others Pay Cash.”

I thought about that this week when I considered the mayor of Minneapolis, Jacob Frey, who asked Donald Trump, as a sign of good faith, to pay the city in advance for what it would cost to host the president’s latest rally.

Frey sent the Trump re-election campaign a $530,000 bill to cover the city’s security costs and the rally’s use of the 19,000-seat Target Center in downtown Minneapolis. Having heard about what’s happened in other cities, Mayor Frey was being cautious and fiscally responsible, trying to get his constituents reimbursed ahead of time, because of the Trump campaign’s history of stiffing or shorting cities on huge security and traffic-control bills. Of the amount Frey is asking, $400,000 would pay police overtime costs.

In June, the Center for Public Integrity, NBC News, and CNBC-TVoo released their accounting of Trump’s more than 60 campaign rallies and the costs not paid back to local municipalities — costs amounting to around $800,000. Many of those unpaid bills were from small municipalities and totaled between $10,000 and $18,000. But El Paso, Texas, is owed more than $470,000 for Trump’s widely publicized rally there last February; and nine other cities across the nation are in the lengthy waiting line for payment.

It’s no wonder people want their money up front: Throughout his silver-spoon life, Trump has left a dirty trail of unfulfilled pledges and unpaid bills. His bad-faith history goes way back. USA Today has found more than 200 liens since the 1980s filed by contractors and workers who said they were stiffed. When Trump owned his woebegone casinos, state regulators had complaints from plumbers and painters, waiters and bartenders, real estate brokers and law firms — 253 subcontractors on a single project, whom Trump failed to pay in full or on time.

Among all his other character flaws, Trump is a four-flusher, the classic casino sneer at a player who doesn’t follow through. How many times have you heard him say he’s going to give a million dollars of his own money to this or that? So, when was the last time he gave any of his own money to a charity? In the past 15 years, Trump promised to donate earnings from a variety of his money-making enterprises: $8.5 million altogether; but, despite all his public pledges, as a billionaire, to “this” and “that,” the amount he actually gave over that time was only about $2.8 million — less than a third of what he boasted.

He boasted that he would give a million dollars to a non-profit group helping veterans’ families. He delayed and delayed until, finally in May, under pressure from the news media, he made good that pledge.

Trump was said to have donated $1 million to victims of Hurricane Dorian in the Bahamas, but Politifact, the Pulitzer Prize-winning fact checker, found that wasn’t true. Perhaps he’ll toss out more paper towels.

He also boasted far and wide about his Donald J. Trump Charitable Foundation, and from 1987 to 1991 he gave away $1.9 million through it. But in 2018 after an investigation by New York’s attorney general, Trump closed and gave away all the remaining assets of the ostensible foundation under court supervision. State Attorney General Barbara Underwood said the foundation was “functioning as little more than a checkbook to serve Trump’s business and political interests,” and engaging in “a shocking pattern of illegality” that included unlawfully coordinating with Trump’s 2016 presidential campaign.

As a four-flusher, Trump’s pledges aren’t worth the paper they’re printed on.

Robert P. Bomboy has written for more than 60 national magazines and is the author of six books, including the novel “Smart Boys Swimming in the River Styx.” He taught for more than 30 years in colleges and universities, and he has been a Ford Foundation Fellow at the University of Chicago and in Washington, D.C.