He is a shrewd businessman and yes he is a fake, he smiles for the cameras but the moment you say or do something he doesn't like he becomes a monster. Even Don King feared Arum, he told a story about when Arum got pissed off he would make people get scared, his whole face and eyes and voice would change and he would curse you out.
Just remember when he told Nacho and JMM to stop crying and they were ****ing up the sport? He also got mad when someone made fun of Hilary Clinton supporting Kelly Pavlik, Arum is a die hard democrat and the guy who made the joke was thinking Arum would laugh because Arum was making fun of republicans but Arum didn't like it and yelling that is BullSh1t! and got super pissed off and told the guy that it wasn't funny or a joke.
I would say the majority of the boxing promoters are slimey guys, Gary Shaw, Don King, Bob ARum, the ones who are cool like Lou Dibella, Kathy Duva, Dan Goossen, Hearn, they are all small time and not on that level, it seems in order to be the top dog in boxing you have to be evil the good guys like the ones I listed below never get to the top like Arum, Golden Boy, King, Shaw.