I have a copy of Murder on the Orient Express by Agatha Christie. I want to post it, but when I looked on the back cover to get the ISBN, instead it says "NOT FOR RESALE". The ISBN is located on the inside cover, and it's obviously not an ARC as this book has existed since the 1930s. Can I post it?

Since it states Not For Resale I wouldn't post it.

Why not?  Sometimes books are used as promotional tools by publisher's.  As long as it is the complete and final version, why not?  The excerpts that are given as freebies are specifically not postable as they are not complete.  ARCs are not as they are not the final version.  This sounds like a promo copy. 

ETA   That said, posting Agatha Christie might be like posting Dan Brown or Stephen King.  How many hundreds of copies are posted?

Actually, it had 2 wishers, all the information exactly the same. The book says "The Adventure Company" on the back. I looked it up. It's a video game line with games based on books. So this must be a promotional copy. So I say postable? It's listed here, with wishers, the copy is complete and unabridged, and it's not listed as being paired with the video game, just the book itself.

Totally postable,, I would be happy with it.

Here are the guidelines from the Help Documents. 

*Based on the guidelines I would venture to say that the book is postable.*

Allowed:

• Paperback books
• Hardcover books (dust jackets not required)
• Audio books (must be originals, not burned copies)
• Ex-library books
• Books with accompanying media
• Textbooks/Workbooks
• Foreign-language books (if in a language other than English, the language needs to be specified in the book description)
• Playaways (these are considered audiobooks)

 Not allowed:

• Anything that is not a book (this includes calendars, coloring books, blank journals)
• Anything that contains advertising
• Advance Reader Copies* (also known as ARC s, Review Copies or Uncorrected Proofs--these are not the final versions of books)
• CD-ROM books/e-books (books that must be read on a computer)
• Burned copies of audio books
• Xerox or otherwise unoriginal copies of books
• Unbound pages
• Music recordings, spoken-word recordings (these can be swapped at SwapaCD)
• leaflets or pamphlets or booklets** without ISBNs (other members complain at spending a credit for these)
• Brochures/Promotional "first chapters" of books - these are not complete books, even if they have an ISBN
• Books that require supplementary non-media materials (non-media materials cannot be sent by MediaMail)
• Pornography (sex manuals and erotica are allowed, hardcore pornography is not allowed)
• Supplementary media alone (without the book they originally accompanied)

*ARCs may be swapped "unofficially" in the Book Bazaar Discussion Forums.  They may not be Posted to a PBS Bookshelf.

**A leaflet/pamphlet is an item with fewer than 20 pages; a booklet is an item with between 20 and 50 pages that is not a children's book. Children's books often have less than 50 pages and are not considered booklets just because of their short pagelength.

Please note: if you Post an inappropriate item for swapping, it may be removed from the database as an automatic action without notice; if it has been requested from you before that happens, you will not get credit for sending it.

I would post it, and PM the requester explaining the situation with the book and making sure it's what they want. I don't know why anyone would decline, but if it's a book with a million copies in the system, and people are wishlisting a certain edition, they might be looking for something specific. Maybe your book is exactly what they are looking for!  It sounds postable, but why go through the headache of a RWAP with a picky requester if it's something debatable.