To add some clarity about this bug:

The Listing's thumbnail image isn't updating to the latest avatar thumbnail. The Listing image is stuck as the original thumbnail the avatar had when the Listing was created.

Since Listing images are cropped differently (square) it would be ideal if we could upload a different image to use for the Listing.

That would be so frustrating if that happened to my products! Big upvote!

This bug still lives! I think the listing is stuck using the first thumbnail uploaded. The listing thumbnail won't update through Unity or VRC's website :/