The primary figure of speech in Sara Teasdale's "Barter" is personification: the assignment of human traits and activities to non-human entities.
The entire poem is based on the idea that "life has loveliness to sell." "Life," of course, is not a person that can literally sell something, lovely or not. The poet is speaking about life as if it were a human being that has something to sell.
A secondary personification is in line 4: "Soaring fire that sways and sings."
Some other figures of speech in this poem are:
Simile (comparisons that use the word "like" or "as"):
a) "Children's faces looking up, / Holding wonder like a cup."
b) "Music like the curve of gold"
Anaphora (repetition of phrases):
a) "Life has loveliness to sell" (at the beginning of stanzas 1