The mods of T_D would never do this but, let's play Devil's Advocate and consider the worst possible scenario:

Trump agrees to do the AMA on an unknown website run by unknown individuals with unknown levels of control. The AMA is advertised, announced, promoted, and everyone is watching.

When the time comes, someone's troll bone goes into overdrive and they decide "for the lulz" to replace the website's banner with an animation of Joe Biden buttfucking Obama, and that's what every international media company sees when they browse over for the AMA.

It wouldn't matter if Trump just turned off his computer at that point. He promoted it, he agreed to it, now he's held responsible for the ensuing scandal and outrage and he looks incompetent for trusting a bunch of unknowns.

Could the same thing happen on any other website? Sure, and there have been some similar embarrassments in the past. But then in that situation the victim goes, "CEO is a respected, long time veteran of the industry, so I thought I could trust them, but obviously was mistaken" or you see someone fired in a very public fashion and they become the scapegoat.

That what Trump and family would need here. They would need someone who has impressive, long-standing credentials that the average person would agree would be someone that you couldn't blame anyone for trusting and taking at face value.