Teasdale doesn't mention happiness directly in "Barter," but we can certainly see it's meant to be a byproduct of the loveliness that she's peddling: Buy some loveliness, and we'll throw in jumbo-sized happiness absolutely free! Let's take a closer look at how that sales pitch works in the context of the poem.
If "Barter" doesn't make you happy, you should seek help. Something might be broken.
Barter is a much more complex poem than it appears at first glance. It isn't just a cute little poem about pretty things.