The whole spine thing confuses me so I am sorry to bother you.  

If a book falls open to a particular page or two, and you can see the pages starting to separate, but still intact (you can see the spine when it flips to these pages) is this RWAP? 

I know that if it isn't, I do not feel comfortable posting the book after I get done with it.

Thoughts?

This confuses me too.  I have never seen a book that favors a certain page that didn't have the spine basically snapped at that page.  My understanding of the PBS rule is that if you can see the spine then it's unpostable. But if the spine crack is there but no spine is showing it's postable.  I've been too chicken to post a book like this to see though.  I mark the ones that have spine showing as RWP and the ones that just have the crack as good.

According to the help center, the guidelines for binding are:

• Must be intact, with no separation on the inside or outside of the book
• If the book tends to open at a particular page, this is OKAY
• Small amount of fraying or denting at top or bottom is OKAY

I'd think your book is okay.  The sender could argue the point with you if you mark RWAP. 

Thanks!  I will report is without a problem but make a note and not repost it. Bummer!