Whether the astrologer deserves every bit of his wages is a matter of opinion. The anonymous narrator of the story is evidently expressing the astrologer's opinion rather than his own.
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 a matter of study, practice, and shrewd guesswork. All the same, it was as much an honest man's labour as any other, and he deserved the wages he carried home at the end of the day.
Although the astrologer is not a "legitimate" astrologer, there is no proof that anyone can read anything in the stars, regardless of how long them may have studied this ancient but spurious pseudo-science. The astrologer in this story provides entertainment for all the passers-by, and he is capable of giving his paying customers good advice because of his "study, practice, and shrewd guesswork." He may not understand the stars, but he understands people.
He had a working analysis of mankind's troubles: marriage, money, and the tangles of human ties. Long practice had sharpened his perception. Within five minutes he understood what was wrong.
In other words, he had found out through experience that most people's problems were pretty much the same. He was wise enough not to offer any advice until he had listened to his customer for at least ten minutes. By then he would understand what they really wanted to hear, and most of his customers left satisfied with the standard sort of advice he gave them.
Another reason the astrologer could feel he deserved the small amount of money he brought home in coins was that he spent long hours at his work. On the day in which the story takes place he set up his "professional equipment" at noon; and:
It was nearly midnight when the astrologer reached home.
Although he had had a profitable day because of his encounter with Guru Nayak, he still only earned enough to buy food for himself, his wife, and his little girl. His wife is delighted because with the few extra coins she can buy a special treat for their daughter. She tells her husband:
"I can buy some jaggery and coconut tomorrow. The child has been asking for sweets for so many days now. I will prepare some nice stuff for her."
There may be many days when the little family goes hungry because rain prevents the astrologer from going to the park. The reader sympathizes with these humble people and cannot help agreeing that the astrologer deserves every bit of his meager wages.