Why did ancient Greek Sophists charge fees for their instruction?

Ancient Greek Sophists charged fees for their instruction because they were professional, independent teachers who traveled throughout the Greek-speaking world to provide higher education. Unlike some other philosophical figures of the time, such as Socrates, who did not charge for his teachings, the Sophists made a profession of being inventive and clever, offering their services as a way to earn a living.412

The demand for their instruction was particularly high in Athens, where the city's democracy created a need for citizens to succeed in public life. The Sophists taught young men how to speak effectively and what arguments to use in public debate, skills that were essential for those seeking political influence. By providing this specialized training in rhetoric and other subjects, they fulfilled a practical role in Athenian society, and charging fees was a standard aspect of entering and maintaining this profession.12