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In “Guys and Dolls,” Sky Masterson’s father gives his son some famous advice: Never underestimate the cider-squirting ability of a jack of spades in a sealed deck of cards. My Grandpa Charlie owned a small dress company, and here’s the business advice he might have given me had he lived long enough to behold Donald J. Trump.

1. Trust the doer over the dreamer: Lots of people talk big but never deliver. Trump talks huge — and has a history of getting things done. New York City tried repeatedly to rehab Wollman Rink and failed miserably. Trump succeeded.

2. Partner with a winner: To Trump, everything is a competition. According to his friend, former New York Mayor Rudy Giuliani, Trump is not a fan of the win-win outcome. The other party must lose. No wonder many who have done deals with Trump have vowed, “Never again.” (Trump is notorious for often paying contractors less than what he owes. He is adept at finding a flaw that, he says, merits a discount. And when he pays, he pays slowly.)

3. Beware of the litigious: If you serve Trump a cold bowl of soup, he probably won’t sue — but you never know. Trump is a bully and sometimes prevails by threatening smaller players with lawsuits. Many can’t afford the legal risk, or the cost. Such ferocious litigiousness can help if you’re Trump’s partner, but Grandpa would have said, “Beware the man who likes to sue. Someday he may sue you.”

Donald Trump pitches himself as a 'fighter'

4. If you don’t know marketing, find a partner who does: Trump is undeniably a marketing genius, both in business and politics. In a financial disclosure form, he valued the Trump name at $3 billion, or $600 million per letter. Well, it is worth something. If Grandpa partnered with Trump, he’d leave the marketing to him. And he’d understand if, in discussing their wonderful project with the wider world, Trump neglected to mention Grandpa. That’s part of marketing, too.

5. Is everything subject to negotiation? In business and politics, Trump’s answer seems to be yes. Flexibility can undeniably be a virtue. But Trump believes facts are negotiable. So his first statement of a fact may be just an opening gambit, subject to extensive revision. What eventually emerges might be the truth. Or not. No, Mexico is not sending us its rapists. (Illegal immigrants are less likely, per capita, to commit rape than Caucasians born and bred in the U.S.) And, no, Trump Steaks does not exist. Trump canceled the trademark two years ago.

6. Beware of leverage and liquor: Those are the two great evils, according to Warren Buffett and Grandpa. Trump, a teetotaler, recently declared himself the “king of debt,” but he probably isn’t. And that’s a compliment, more or less. (Although he did recently add new debt of at least $50 million and now owes at least $315 million.) In the old days, though, love of leverage helped cause him to declare bankruptcy four times on various properties. When the real estate market cratered in 1989, Trump was so many billions in the hole that it was in the banks’ interest not to force him into bankruptcy. They put him on an allowance instead.

7. It is essential to understand how a person defines winning: Trump says he made money from his Atlantic City, New Jersey investments. (He charged his casinos for using his name and made them buy Trump Water.) But the investors who owned stock in his casinos or held their debt lost big. And Trump stiffed some small contractors who serviced the casinos. However much cash Trump pocketed in Atlantic City, his former partners and vendors don’t want to hear about it.

8. Does a person know his limitations? Trump is smart and in the last year has demonstrated political chops most of us have never seen. But some business associates, including admirers, have said he doesn’t seem to know what he doesn’t know. A quick study, Trump apparently thinks he can be an expert on anything. CEOs and presidents must be quick, but even more important traits are the ability to delegate and to referee astutely when aides disagree. All this would lead Grandpa to ask: Does Trump work with at least one person who can tell him he’s wrong? Reportedly, daughter Ivanka has urged Dad to act more presidential, but in this realm the verdict is clear: Dad is not a quick study.

9. Is he a master of new media, like color television? Yes, Grandpa, he is. And Twitter, too.

“ In assessing Trump, Grandpa Charlie would want to know how much is upscale packaging and how much is the real deal. ”

10. Beware of a person with something to hide: Don’t hold your breath waiting to see Trump’s income tax returns. It’s a fair bet that, absent a change in the law, they will remain secret. Trump has clearly concluded his returns are not good for his political, and perhaps even business, brand. And Trump protects his brand like a mother bear guards her cubs.

11. Learn about a person’s worst deals, not just his best: Given the value Trump places on his brand, some of his ventures have a startlingly unsavory, what-was-he-thinking quality. By any standard, the now-defunct Trump University was a disaster. Around 7,000 former Trump University students are suing for damages. A multi-level marketing project called The Trump Network was arguably less of a fiasco, but in May a Harvard University doctor toldThe Daily Beast it was a “scam.” Participants took an expensive urine test and then paid up for supplements — of unproven merit — supposedly tailored just for them. What reportedly clinched the deal for Trump was the upscale packaging of the product. That venture ended in 2011.

In assessing Trump, Grandpa Charlie would want to know how much is upscale packaging and how much is the real deal. And he’d probably say, “If you don’t know, you either better do more research or look for a different partner.”

Andrew Feinberg is the author of “Four Score and Seven,” a novel which imagines that President Abraham Lincoln has come back during the 2016 U.S. presidential campaign to interact with a character who, some say, resembles Donald Trump. Learn more about the book and author at MissingLincoln.com