I ordered two books in a series from the same member.  She sent  one book, the first in the series,  but mistakenly sent me a different (and unwanted) book  instead of the number two book in the series.  I marked it RWAP and in the pm asked her if she still had the other title, the one she should have mailed to me.  She replied that she cannot find the other book  and, thus, won't be able to mail it to me.

Okay, it's now nearly 3 weeks later.  I pm'd the sender  after my first forum post and asked her to contact PBS admin to cancel the transaction.  I never heard a word from her and the book remained on my account page.    Then PBS declared the book lost in the mail around 10/29 and refunded my credit.  In the meantime, I ordered the book again from another member and it's enroute to me now.

In yesterday's mail, I received the originally-requested book along with a copy of a pm between the sender and another member to whom she had sent MY book in error in which she was asking the person who received my book to mail it to me and she would compensate her.

If the sender had pm'd me that the book was being mailed to me by the member to whom she'd mistakenly sent it, I would have been okay with that.  But since I didn't hear a word from her, I reordered the book. 

How should I handle this?  Am I obligated to go to my archive and mark the first book received?  I don't want to because I ordered the second book when I got no response to my pm to the sender about contacting PBS admin.

Thanks!

You have done the correct thing.

From here, your two options are:

1. Have the sender notify PBS that the book order should be cancelled. (You can't do it, only the sender can).
2. If the sender won't cooperate, then you wait for the book to go lost in the mail.

Either way, you will get your credit back.

What Sara said.  The receiver cannot cancel the transaction, but the sender can request PBS admin cancel it.  Otherwise, the only option is to wait for the system to time-out and mark it lost.  As mentioned, you get your credit back either way...it's just faster if the sender will cooperate and request the cancellation.