I received a book deal that required me to request 3 books but one of the books I requested wasn't in the box.  There was however one book that I didn't request in the box.  I have marked received on the other 2 books.  What do I do about the missing one and the extra one?

I would PM the sender.  She probably mixed up your order with someone else. 

There's a couple of ways to handle it.  If she doesn't respond then you'll get your credit back for the 3rd book when it goes lost.   Then you can just the incorrect book to your shelf or donate it.   If she still has the 3rd book she can send it to you and you mark it received through the Transaction Archive if it goes lost before it gets to you.  If you got someone elses book-she can give you a credit to cover the postage of sending the book to the right person.  She can then give a credit to that person to cover the postage of sending the book you ordered to you.