Yes, you have to decide if you want to ask for your credit back or not.  It would be a grey area for me.  The member might not have read the book and you said it was good, so they may not have noticed. 

It can't be posted again, so yes, RWAP.

If it was a  keeper for me, I would RWAP and not ask for my credit back. If you wanted to swap it here though and now can't I would RWAP and ask for your credit back as we all need to be super careful about what books we mail.

You can always post it in the Book Bazzar describing the damage and still ask a credit for it.  Lots of members are willing to take damaged books as long as they know ahead of time what they're getting.  That's a good option if you have already marked it as received.

If you're going to keep the book & would rather not RWAP- maybe at least mention it nicely to the sender. You could save them from another member's ranting at them about the same thing in the future! They may not have read the book to notice, could have been overlooked. If it bothers you or if you want to repost-definitely RWAP.