I ordered a children's. The description said the book had stickers. The stickers were missing from the book (just the blank pages where they used to be). Should is this ok and could I repost it? Or should I mark it reicived with a problem.

I believe stickers would fall under the non-media materials. If the book is not usable without the stickers, then it shouldn't have been posted. It the book can be read without the stickers, then it is postable without them. 

You can search the Help Center for accompanying non-media material and you will find more detailed explanations.

The following excerpt is from the Help Center > Browse Help Docs > Posting Books > Is my book okay to post here?
YES means postable, and NO means not postable.

Books that require accompanying NON-Media Materials to be usable: NO 

• Non - media items cannot be sent by Media mail
• Example: a book that requires a decoder for its proper use.  Such a book must not be posted here.

Books that originally came with NON-Media Materials that are not necessary for the book to be useful: YES and the non-media items are not required to accompany the book

• As long as the materials are not REQUIRED to use the book (ie, jewelry), these CAN be posted here. 
• The requestor should NOT expect original non-Media items to accompany the used book.

In addition, from Help Docs  > Browse Help Docs > Posting Books > What can be posted for swapping here?

Allowed:

• Books with accompanying media (the accompanying media must be included with the book)
• Books that originally came with non-media items, if the non-media materials are NOT REQUIRED for the book to be useful.  The non-media items do not have to be included to be postable here

Not allowed:

      *  Books that require supplementary non-media materials to be useful (non-media materials cannot be sent by MediaMail, and original non-media materials cannot be expected to be included with a used book)

You can go to the Help Center references above for additional information, but these excerpts seem to be the most relevant to your question.

Thank you  Chris and Melanie. It still seems a little ambiguous, being the stickers were pasted onto the pages in the book they probably would have passed the Post Office test for media. But I will mark it received and just not repost it.