I ordered 5 wishlist books for 5 credits from a single PBS member who posted them to me directly.  But when I received the box, it contained only 4 books. 

I'm not overly concerned about the transaction, I'm sure it was some sort of honest mistake and have PM'd the PBS member.

I'm posting becuase I'm curious about how to handle it. 

On the other 4 books, it didn't seem right to mark them Received with Problem. Even though the box was short one book, the 4 that arrived were fine.  So I accepted the 4 and left the 5th hanging.  If the member can't find the book, or honestly thinks she shipped it, what happens? (She was offering a bunch of books, it may have gone in someone else's box. Mistakes happen sometimes.) 

Do I just let it hang out until declared lost?

That ties up a wishlist book for me for quite awhile, but luckily I don't care too much about that.

Yes, you leave it until it goes lost (or until you receive it! Let's be positive! :) )

You can't mark a book RWAP if you didn't Receive a book, after all! :) 

The sender has the option to contact PBS and cancel the book order after it is marked mailed.   Otherwise you have to wait for it to go lost.

Yes, each book is a separate transaction, even if they are mailed together.

So, you mark 4 received, and one will go lost in the system unless the other member asks PBS to cancel it earlier.

What Sarah said.

 You did the right thing.

 Marked the 4 you got as recieved,

 PMed the member about the problem.

 Now you wait.

 PBS should be named patientbookswappers.com  to remind us all of this wonderful game we play!     :)

She probably stuck it into someone else's book order.

Kim, that's hilarious.  Gotta remember that one.