Per guidelines, I PMed the condition of the textbook (minor highlighting in the beginning, otherwise unmarked and in great shape). I assume I need to now wait for a response, but how long? I chose two days (in hindsight, I should have chosen longer), and want to mail tomorrow. If I don't hear back before then, it's Sunday and the PO is closed. Monday, the transaction will cancel. What to do?

You will have to cancel, or actually, let it cancel, if they do not get back to you. You cannot mail it without them agreeing to the highlighting/writing. If they don't want it, then you have to give them their credit back, and lose the postage too. The system does actually give you an extra 48 hours after you say you are going to mail it, so the time/date on the item on your front page, should be a bit longer than the two days you picked, so there should be time yet for them to answer. But, if they don't, you should let it cancel itself out. Or cancel it at the latest minute before going to bed, so that you can state in the reason for cancelling that you did not receive an answer on the highlighting/writing, so that if there is a question somehow, it is on record. UNFORTUNATLY not really what you wanted to hear  :(

but I thought because it was a textbook that writing and highlighting was allowed and it should be expected.  oh but I guess you have to let them know because it is a textbook it has it in there. 

I would think they will get back to you especially if it is a book they need!

From the help center

writing or highlighting on the text pages is NOT OKAY

• Exception: if it is a textbook or workbook, these are expected to have highlighting/writing
  • if you post a textbook/workbook, the condition must be described to the requestor in a Personal Message
  • AND the described condition MUST BE AGREED TO before the book is sent

Leslie, whenever you post a textbook, you have to PM the requestor with the condition of the book, and they have to agree to that condition.

By the way, I got a response pretty quickly. :)