Hello dear Crystal group managers,
As Crystal gains more visibility, more spam posts are getting into Google Groups.
While there have been other suggestions (migration to Discourse and similar), there is a quick fix that can be performed to reduce this.
You can find this under Manage > Settings > Moderation, and adjust "New member restrictions" to "New member posts are moderated"
You can find more details here:
That will be a great improvement from the current flood of spam listings that are getting into the group.
Thank you,
Luis Lavena