Trump is incredibly miserly for someone who's so terrible with money. He straight-up refuses to pay anyone he thinks won't win a lawsuit against him, stiffing dozens of contractors who worked on his real estate projects over the decades. He even ghosts the venues that host his rallies when it comes time for his campaign to repay them.

There was an experiment where checks were mailed weekly to various random wealthy people with slightly less each week to see at what point they wouldn't even bother cashing them in. Trump was one of only two people to keep cashing them even when they dropped to pennies per check.

He's also infamous for lying about his wealth. He is (or was before his presidency gave him endless opportunities to grift) a paper billionaire who in reality was so deep in debt and had such bad credit due to his constant bankruptcies that no bank in America would lend him money. That's how he got involved with Deutsch Bank, the one with shady connections to the Russian government.

He's corrupt, incompetent, and willing to do anything for money. And he has so many grifts running that even if they aren't making much individually, he's still "earning" a fortune overall.