When we shop we make choices: brands, styles, price. In "Barter," Teasdale is asking the reader to choose loveliness. She wants us to buy what life is selling. She offers examples of loveliness to try to influence the reader's decision. She makes a pretty good sales pitch, but ultimately it is up to each of us whether or not to choose loveliness.
Teasdale should stick to poetry, because she is the worst salesperson ever. The world is filled with so many wonderful sights, sounds, smells, and tastes and yet all she could come up with was waves and the smell of wet trees? Weak effort.
"Barter" is a great deal for readers because, by using simple, universal, beautiful images, she reminds us that loveliness is right in front of us all the time.