Was the DC on the first book scanned and showing under the details? If it was, I don't know why she would have said she didn't mail it yet. If I'm misunderstanding, let me know.

Normally they tell you to put the book on hold for a while in a case like this. It would be nice if the system automatically did this for you in the case of a lost book, but yeah. That's a different subject. In this case, since it went back onto your active WL and you now have another offer, I wouldn't cancel or let it time out, as you'd lose your place at the top of the WL. You could either accept the new offer, or use the CONTACT US link to ask that they cancel it for you and keep you at the top of the WL.

If you do accept the new offer, the second person would receive the credit and you are not obligated to give a credit to the first person. They caused the mess, not you or the second sender.

One more option, is the new "not now' button.  This will put the book one hold on your wishlist and offer that copy to the next wisher. 

I'm a little unclear about watching the book travel...was that via the little truck (estimated) or actual scan details?

IIRC the guidelines say to wait 14 days after a book goes lost before re-ordering.  If that amount of time has elapsed the requester is not required to mark the first book received...not sure what happens if you are notified (and accept) of a late mailing, and if it effects the dates.   With proof of that late of a mailing, marking it received is optional IF you have already received another copy.  Otherwise, the receiver is required to mark the book received regardless.

If the first book arrives, make sure to mark it RWAP for being mailed late.  And probably contact TPTB regarding the pm also so they can keep an eye open in case this is a chronic late mailer.

ETA - at this time USPS.com has no scans whatsever for that DC number.

Did you click on Details and see the actual scan for delivered? The page for the little truck is just for fun and does not show actual delivery. From what I see above in the transaction details, the book was marked mailed and never scanned. And she admits she didn't mail it. You can accept the new offer for the book and you don't have to give the first sender a credit since she mailed late (Or not at all). Or you can hit Not Now and the book will go to the next person in line but you won't lose your place in line.

I'd accept the wishlisted book and deal with the possibility of getting two copies as it doesn't appear the first member actually mailed the book. Then if I got two copies would just repost one of the copies.

I'm with Rebecca.  If the original sender says she didn't mail the book, then who's to say she mailed it after you contacted her?  Something isn't adding up.

She hasn't mailed it.  9452 numbers don't show up on usps.com, but you can see the scans under Details on the transaction or by going to paperbackswap.com/track. 

Entering this number shows

Tracking Number: 9452110200817011002086
Status: New Item
Message: The tracking information for this item was received by the US Postal Service at 9:39 AM on 01/25/2013 but the item has not yet been scanned in the mailstream. Please check back later.

She hasn't mailed it. 9452 numbers don't show up on usps.com, but you can see the scans under Details on the transaction or by going to paperbackswap.com/track.

Lack of scans don't confirm lack of mailing, it only confirms...a lack of scans. There are often books that travel the whole distance with no scan but the delivery scan. It just means it didn't go through a sorting facility along the way.

Using the Not Now button is the best option in cases like this. I'd also PM the member letting them know that I've done that and they need to have mailed the book. If they haven't done so, then they need to let me know and I would be taking the wish back off of hold in 14 days and if the book isn't to me by then they would not be getting the credit.

Was the water damaged book from the second sender?  Just in case, did you double check the return addy  to make sure it wasn't sent from the first person? In that case, the second one may still be on the way.

Did you RWAP the water damaged book (make sure you have the right transaction)? That will put you back on the WL in first place and you can get a better copy.

If it was the first book then use the transaction archive to mark it RWAP. Be careful that you have the right transaction.