Test every realtor at the time with this same standard, and see what you find.
Hogspittle.
The book was a fascinating compilation of his various interviews with Chicago people who performed various jobs in exactly the era we are talking about.
I cannot imagine that New York would have been too different.
Anyway, he devotes an entire chapter of that book to covering a lady who called herself a professional neighborhood preserver. What unscrupulous real estate agents did in those days was to find the worst Black family or excuse for a family they could and sell them into a white neighborhood, even at an economic loss if necessary. Then, after a few weeks of petty vandalism and burglaries, they would go around to other houses in the neighborhood and offer to buy them out for cheaper and cheaper by pointing out what was happening, even if the subsequent Blacks buying in the neighborhood were normal decent people who just wanted out of the hood.
By constantly targeting and churning neighborhoods in this fashion, they could keep their commissions flowing and make money from both the Black families moving in and the white families moving out (and into another neighborhood somewhere else).
The "neighborhood preserver" lady wasn't the least bit racist, she just wanted to educate her neighbors on what was happening so they didn't fall for this shtick.
Legitimate realtors (which, I would bet, includes the Trumps) were left with a Hobson's choice of either defying the government or being accused of block busting and churning as the unethical realtors were doing.
Most of them simply chose to ride the fence via the tactics described so they would not run afoul of either group.