i find it extremely hard to imagine that Donald Trump would have ever been personally involved in the sale of a vehicle at the level that he'd be making decisions about whether or not it was detailed, but I guess it's sensible generic advice
It’s not that a car needs to be clean per se, but you don’t want prospective owners to be distracted by thoughts of the past life the car has had in the care of another human. Nobody wants to touch the indicator stalk that has layers of dirt and finger grease baked into it.