He had 500,000 reasons to deliver sunny testimony in Trump’s civil fraud trial, according to a Trump biographer. David Cay Johnston, who authored the book “The Big Cheat,” recounted on CNN’s “Anderson Cooper 360” how New York University Professor of Accounting Eli Bartov was compensated handsomely to appear as a witness to paint Trump as a model executive in Trump’s $250 million trial brought by New York Attorney General Letitia James accusing the tycoon of building his real estate empire wealth using widespread fraud. “I was frankly, very surprised of this very eminent accounting professor’s …