the sender has not marked it mailed.  Plus, I believe it is water damaged.  Does water damage always leave a stain?

This book is NOT stained but the top half of the first 65 pages are all bumpy and wavy like it had been wet.  It's a book I would not pass on.

Do I just wait for them to mark the book mailed or PM them about my problem and hope they read their messages?

Hi Becki,

Usually in this situation, there is a sender who didn't mark the book mailed in time and the system re-requested the book for you (the book currently on your My account page).  Check your transaction archive (blue link on your My Account page) and see if you see the same book listed with a red X out to the left.  If so, this is the book you've received.    If it isn't in your transaction archive, then the current sender has not marked it mailed yet. 

This Help Center Topic talks about how to handle this situation.

Water damage doesn't always leave a stain; however, it almost always has a different texture feel to it (a bit more stiff).  A lot of newer paperbacks are made with lower quality paper that has a tendency to get wavy easily even when not wet.

This may be helpful:

I got a book I requested, but I can't mark it received!