There is a sense of impermanence in "Barter." Many of the images that Teasdale uses as examples of life's loveliness are fleeting things—here one minute and gone the next. We definitely get the feeling that the loveliness for sale is a limited time offer.
We should take "Barter" at face value and stop trying to make everything so emo. Teasdale isn't trying to show us impermanence or the fleeting nature of beauty; she's just trying to get us to appreciate the world around us. This is a simple poem with a simple message: appreciate life.
The combination of sweetness and urgency makes this a great poem. It's like dipping a salty fry into a vanilla shake—the sweet and salty balancing each other into perfect blended flavor. In fact, without that secondary saltiness of urgency, this poem might be too sweet to stomach.