I recently had a transaction go astray. A sender switched books and I got the book intended for another PBSer, and vice versa. We were able to get it fixed, and I sent the book to the right person and she sent me mine, and the original sender is supposed to buddy us both credits.

I received my book today and it's the wrong version - the transaction archive says hardback, while I received the paperback. In checking the ISBN, this book has the HB ISBN on one of the inside pages. But above the bar code is the correct PB ISBN. The bar code was covered up by a price sticker (looks like it came from Borders).  Unfortunately, the lister went with the ISBN inside the book, ignored the pop-up box to be sure the version matched, and listed it anyway. If she'd pulled off the sticker (which came off quickly with no residue for me), she'd have seen the right ISBN.

the ISBN inside the book is usually the right one...this is one of those rare occasions where there was a misprint or something. 

but yes, good reminder to make sure what you are posting matches title, author, isbn and binding!

And, it doesn't matter if she didn't see the right ISBN or not, since she ignored the popup and posted the book incorrectly, you need to make sure you mark the book Received With a Problem and ask for your credit back. Wrong binding is an official reason for RWP and for asking for your credit back according to the Help Center.

Here's the HC link:

There is a problem with a book I received!

Already marked it RWP since I got the other person's book instead. I've just notified the original sender of the problem with the version, too. She said she'd buddy us both credits, so I hope she lives up to her end of the bargain.

For future reference, if you receive a wrong book because the wrappers are switched, in addition to all the things you three did to work it out, you can wait to mark your book received when it finally gets to you.  You don't have to mark it Received with Problem unless, as in your case, the book actually has a problem when it finally arrives.