How do you make so much $$$ Money?

A teacher, doctor and a businessman attend a party. A teacher and a doctor meet each other and as they were having a conversation, they see a well-known rich businessman. Thinking of giving a try to converse and get some advise from businessman, they both approach a businessman by introducing themselves and ask,

Teacher: Sir, if you don't mind: How did you make that much fortune?
Businessman: I bill people for giving advise.

Teacher and a doctor nodded with an agreement and carried on their conversation. Couple of days later, they both (teacher & doctor) received a bill from a businessman.