As the old aristocracy had been replaced by democracy in Athens,being successful in the public arena (for example, in the courts where various cases potentially involving profit often were made) became increasingly important. Where once birth had entitled certain people (the nobility) to the goods of society, now they had to be personally won through rhetoric (the gift of gab?). Those who were particularly gifted at persuasive argument and its corollary, useful knowledge, were in high demand. Such individuals (called Sophists) often would share their skills and practical knowledge for a fee.
Three such Sophists in Socrates' time were Gorgias,
Prodicus, and Hippias.
Both Plato and Xenophon
report that Socrates rejected such fee taking,
opting instead for a free exchange of ideas, as it was an obligation, not
a prerogative, to share important things with other citizens so all could
benefit. Before Socrates may appear too noble
on this point, however, it should be pointed out that he did upon occasion
accept food as a gift for engaging in discussion. It's left to the reader
to make judgment as to the relevancy of this distinction.