Philosophers like Plato and Aristotle were scholars and would make much of their income off of private tutoring for private students, one if the most notable examples being Aristotle teaching for the Royal Family of Macedonia and Alexander the Great. Some would write books, yet this was before the invention of the printing press so books would not be widely distributed. Aristotle was notable for opening a library to more widely display books he wrote.

So most philosophers would make their money from private schooling of students, sitting around at talking politics and philosophical ideas would have been part of this tutoring as well as talking with other scholars.

I believe there was a similar question a while back ill try find it. long story short they taught government leaders/public figures how to act ect