What are the personality traits of the astrologer that make him successful in his profession in Narayan's "An Astrologer's Day"?

First of all, it will be hard to establish that the
astrologer was in fact successful in his profession. The narrator says specifically that
 the astrologer is not a true astrologer:

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he had not the least intended to be an astrologer
when he began life ; and he knew no more of what was going to happen to others than he
knew what was going to happen to himself ... . He was as much a stranger to the stars as
were his Innocent
customers.

True astrologers
in India are most often of the Brahman class who have studied under a guru for extensive
periods of time and attained various levels of mastery. So, in the strictest sense, it
is not possible to say that the astrologer was a success at his profession because he is
what we would call an impostor or a charlatan and not a bonafide member of the
profession he claims. Nonetheless, within the text are some indicators for the success
the astrologer has as a charlatan astrologer who fools his
customers.

The first thing that makes him a success is his attire,
both the garments he wears and the religious symbols he paints on his
face:

He wound
a saffron-coloured turban around his head.
His forehead was resplendent with
sacred ash and vermillion.
This colour scheme never
failed.

While recognizing
that attire is not a personality trait, the narrator’s description of it reveals the
astrologer’s personality traits of sagacity (i.e., discernment and judgement) and
empathy with (i.e., identifying with) others’ perceptions. This is born out in other
parts of the story, for instance when the narrator says the astrologer “said things
which pleased and astonished everyone” as a result of (1) studying the person talking,
(2) long experience (“practice”), and (3) “shrewd guesswork.” Studying people and
“shrewd (i.e., astute, keen) guess work” go hand in hand with the personality traits of
sagacity and empathy.

Another personality trait that the narrator
reveals is that of feeling true guilt: "I thought I had the blood of a man on my hands
all these years." If he did not feel truly guilty for stabbing his acquaintance over a
drunken gambling incident, he wouldn’t have had the impetus (i.e., driving force) to
make a successful living at something entirely outside the realm of his previous
knowledge and experience. In other words, his sense of true guilt made him understand
that he dearly needed a good cover and new identity; others may have continued in a path
of error and wrong doing.

The astrologer’s closing conversation with
his wife reveals another personality trait that contributes to success in his chosen
work, that of being able to focus deeply on the thing that is important at the moment.
For instance, this personality trait is at work when he listens intently to a new
customer: “[he] never opened his mouth till the other had spoken for at least ten
minutes.” Another instance of this trait of focusing intently is that after meeting his
victim face to face again; after realizing that he is now free of guilt; after
deflecting the victim's vengeance; and after making a confession to his shocked wife
(“You tried to kill !”), he can still focus on the immediate moment and what is needful
in that moment and give himself a good night’s rest so he can be an astrologer again
tomorrow.