Laura stared but did not stir, Long'd but had no money:
Laura would love to reach for the fruit, but she doesn't "stir" from where she is because she's strapped for cash.
The repeated "buts" in these two lines help to emphasize the contrast between what Laura desires, and what she can actually have.
The whisk-tail'd merchant bade her taste In tones as smooth as honey, The cat-faced purr'd, The rat-faced spoke a word Of welcome, and the snail-paced even was heard; One parrot-voiced and jolly Cried "Pretty Goblin" still for "Pretty Polly;" – One whistled like a bird.
A couple of the goblins that were described before, in lines 71-76, step up and invite Laura to "taste" their fruits, at the very least.
The one with a "tail" has a voice that sounds as sweet as the fruits look. We're starting to wonder what kind of a "tail" it is – forked, perhaps, like a demon's?
The goblins all sound like the animals they resemble.
There's even one that sounds like a parrot, but he says "Pretty Goblin!" instead of "Pretty Polly," or, as we usually say, "Polly wanna cracker!"