The old don’t pay a hooker by check, Jerry Springer problem.
I don’t know if he was a cheapskate. There were all kinds of rumors about him being a Russian plant, pee tapes, Russian servers at Trump tower etc.. I think the DNC/Clinton/FBI/Steele Dossier had 18 or so various allegations but at the time nobody knew for sure who was behind all those innuendos. Trump hired Cohen to track down these rumors and collect any evidence - according to Cohen’s own Congressional testimony.
Trump didn’t really save any money on this. He paid Cohen twice as much as Cohen paid. And Cohen paid to buy the exclusive story rights. Trump Org maybe put it down as “legal fees” when they should have put it down as an asset purchase. You buy a story, it’s an asset not an expense. But it was Cohen who bought the story and billed Trump. The state has to prove Trump knew it. And even if they did, this alone is barely a crime; a misdemeanor. Sure maybe a year in jail and a $1,000 fine (at least, in my state).
Now if Junior is saying he forged his dad’s name, or otherwise had access to sign checks in his own hand... it creates further lengths to prove Trump knew all the details of the pattern and practice. Trump was running for POTUS and the nomination. His son was running the company.