Is there a way I can review Guestbook entries before they are shown publicly?
Yes. You can enable the Post Approval feature for your Guestbook service, and this will give you a chance to approve the messages before they are made public.
1. Log into your Bravenet account and click on "Guestbook" in the list of registered services
2. Click on "General Settings"
3. Click on the "Security" tab
4. Beneath "Enable Post Approval?" select Yes
5. Click on the "Save" button