Astrology is a pseudo-science. No one can tell anything about human affairs from reading the stars. The stars are millions of light years away. They have nothing to do with our lives, in spite of the fact that many people believe they do. What is the difference between a "real" astrologer and a "fake" astrologer? The real astrologer may give exactly the wrong answers to a client's problem because he is not listening to the client but consulting some meaningless charts. Whereas the astrologer in Narayan's story looks and listens. He pays no attention to the stars or to the charts. He is effective because he pays attention to people. He is a better astrologer than most astrologers.

...he knew no more of what was going to happen to others than he knew what was going to happen to himself next minute. He was as much a stranger to the stars as were his innocent customers. Yet he said things which pleased and astonished everyone: that was more a matter of study, practice, and shrewd guesswork.

People for the most part are only seeking confirmation, validation, encouragement, agreement, permission. If you listen to them long enough, they will tell you what they want you to tell them. When you tell them what they want to be told, they are pleased and believe they have gotten their money's worth. That is why the astrologer considers his profession "an honest man's labour." He is trying to give honest advice. Many people who offer advice for a fee do not always give advice that is honest. Instead, they may offer advice that will be beneficial to themselves.

In "An Astrologer's Day," the main character is the astrologer. He makes an honest living by telling his customers what they want to hear. Even though the astrologer cannot tell the future, he is shrewd in his ability to answer his clents' questions. First, he allows his clients to talk about their problems for at least ten minutes:

Within five minutes he understood what was wrong. He charged three paise8 per question, never opened his mouth till the other had spoken for at least ten minutes, which provided him enough stuff for a dozen answers and advices.

No doubt, the astrologer learned all that he needed to know after his clients had spoken for ten minutes. He had a keen perception of what a person was going through after hearing him speak about his problems. 

The astrologer satisfied his customers. They paid him their money and left feeling better just having someone hear their problems. Sometimes it helps just to have someone hear one's problems. 

Although the astrologer admitted to himself that he could not really tell one's future, he was a good judge of character and after listening to his customers, he knew what to say to satisfy his customers:

He had a working analysis of mankind’s troubles: marriage, money, and the tangles of human ties. Long practice had sharpened his perception.

The astrologer felt he had earned a honest man's labor by listening to his customers and then expounding on what they had told him. He gave his customers their money's worth.