Educated guesses no doubt. There's been reams of uncomplimentary accounts, quite detailed in many cases, written about Trump's business and family affairs of questionable legality by those who knew, or know, him, including by his relatives and his former personal lawyer. He or his business has been fined numerous times for breaking civil laws, and he has already been identified in at least one criminal indictment as unindicted co-conspirator 1. He's been a party to thousands of law suits. Civil, if not criminal, law violations run in his family. His father barely escaped prosecution for "profiteering" during the Eisenhower era, and skirted the limits of the law throughout his "colorful" career. You'd have to be pretty poorly informed not to know these things.