Filtering Posts before they turn public!

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Hi,
It's the first time that I’m using this kind of service. Actually I find very useful. But I would like to make this question, since I know from friends, that they had problems with their guestbook with annoying advertisement.

So the question is, is it possible to see the posts before they turn public, I mean that no one will see the post before I check if is OK to be publish in my guestbook.

Thanks in advance.