First selling anything oil , widgets , or anything is basically the same thing. It only needs someone to know the basics of business . The laws of supply and demand. You don't have to know everything about what your selling.
But being a politician does need someone who knows how to be a leader something Trump hasn't got a clue about and proves that everyday. He had no prior experience ,was never a mayor ,a councilman . a dog catcher . he never before ran for any office or held any. To have a clueless know it all as president was only ever going to be mistake.