Theory:

It was evening. The garden hedge was all aflower.
The fair maid came out and said, “I will hire you with a smile.”
Her smile paled and melted into tears, and she went back alone into the dark.
Explanation:
 
The speaker, having rejected the job offer of the king and old man, walks on in pursuit of a person who could hire him. The rejection of the king and the old man already signifies that he had rejected power and money, the two things that most human beings consider as an important part of their life. But by the time he does this, it is already evening. Any person who is desperate to get a job would pounce upon the next opportunity that comes across him. But the speaker is determined to get a job that allows him to enjoy the freedom that he wants.
 
It was evening and the speaker keeps walking until he reaches a garden. From a path of stones, he earlier reached a crooked lane, and then he reaches a beautiful garden, which shows that he keeps progressing and moving into better prospects of getting hired. The garden hedge was filled with flowers. The hedge, which acts as a boundary is already filled with flowers, which is similar to the speaker establishing his mind regarding boundaries. From the beautiful garden emerges a very fair girl, who also liked to hire the speaker. She says that she would hire him with her beautiful smile. After power and money, people value beauty. The speaker's third test with beauty also yields success as he very confidently rejects it.
 
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Garden with hedges
 
The maiden's smile soon becomes pale and melts away as she slowly walks into the darkness to fade away. This signifies that the idea of beauty in the minds of human beings is flawed. The idea of a fair skinned girl with long hair, beautiful eyes and very slim is etched in our minds. But once we fathom this idea of beauty and accept that people of all colours and weight are beautiful, we might fathom into looking at it as a non-asset. Until then, the poet seems to emphasise that external accepted beauty may fade away. It is temporary and is not worth for the speaker to get himself hired.
 
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Beauty does not have set standards and is temporary
 
Meaning of difficult words:
 
S.No
Words
Meaning
1
HedgeThe boundaries of a garden which is filled with shrubs and trees
2
AflowerFilled with flowers
3
Fair maidA beautiful woman
4
PaledBecome white due to fear or any extreme emotion
Reference:
National Council of Educational Research and Training (2008). Honeydew. The Last Bargain- Rabindranath Tagore (pp.73-74). Published at the Publication Division by the Secretary, National Council of Educational Research and Training, Sri Aurobindo Marg, New Delhi.