I received a book a couple of days ago and I was in a hurry so I just scanned the pages to make sure they weren't wet or such. Last night I opened the book to start reading it and discovered that on the opening page it said "advance reader's edition, uncorrected proof". I then flipped it over on the back and the back doesn't look like a regular book back. The top says "advanced, unedited reader edition", then it is divided into two columns. The columns explain about the book in a small blurb, then about the author, next part is about "best-selling points" and finally "marketing highlights". Was this book postable? I have never received a book like this. If it is not postable, is there anything to be done about it since I marked it received without a problem a few days ago? Thanks for your help. 

IT was an unpostable ARC.

I would PM the sender, explain that ARCs are not postable (cut and paste that section of the HC), explain that you hit received instead of received with problem in error, and ask for your credit back.

Advanced Reader's Copies (or Editions), known as ARCs, are not postable.  There may be changes made to the text before the publisher publishes the book, so an ARC is not considered the final version of the book.

You could find the transaction in your Transactions Archive (on the horizontal yellow bar on your "my account" page) and gently let the person know about the book.  (It's quite possible that the sender did not take a close look at the book and didn't realize it was an ARC.)  You can ask if he'd be willing to refund your credit, if you like, or you can just give him the information.  Up to you.

ETA: Sherry beat me to the answer :-)

It is against the rules to post ARCs here as they cannot be "sold" and PBS credits have what could be deemed "monetary value." You can offer them as freebies in the Book Bazaar and you can also post them on Bookmooch as long as you note in the condition field that the book is an ARC.