I requested a book, got a pm that it has some underlining and highlighting as it is a textbooks "as I can imagine" [I hadn't imagined that actually], did I still want it?  I pm'd back to ask about how many pages and then right away noticed that the request had been accepted and printed.  So now what?  I didn't say I wanted it, didn't say I didn't want it, just asked for more info to make a decision.  Do I have to accept it if it arrives?

[update in my next post]

I would say mark it recieved with a problem.  The Help says

If a member considers her book a textbook she may Post it with underlining/highlighting/writing on text pages, according to the "textbook exception" in the Book Condition Criteria for 'Swappability' at PBS; BUT since the textbook exception in the Book Condition Criteria for 'Swappability' at PBS require her to contact the requestor and obtain PM consent to the book's condition, she won't be in the position of sending a "stealth textbook" to someone who doesn't expect to receive one.

The sender didn't "obtain PM consent" so she shouldn't mail it.

So now I got a reply that the original message was meant for another member [presumably about another book], sent to me by mistake.  This book, that I requested, was also used a textbook but has "only a couple of underlines and is in good shape, sorry for confusion."  I pm'd back to ask again, about how many pages have underlines, no reply yet. 

Then that PM wasn't sent to you by mistake.  ANY highlighting, underlining must be approved by you before the other person sends it.  I would make it clear you want to know exactly how much underlining is in the book before it gets mailed, otherwise you'll be marking it RWAP when it arrives since you didn't agree beforehand to accepting the book with underlining.