Another member ordered a textbook from me the other day.  It had some writing and underlining, so I sent her a PM to let her know and ask her if she still wanted it.  I'm supposed to mail it by Wednesday, and she hasn't responded yet.  I know I still have a couple of days, but in this situation, is there anything you can do if they don't respond to the PM?  I won't mail it yet since she hasn't agreed to the condition, but if she doesn't respond, I'll have to cancel the transaction and my book will lose its spot in FIFO.  It just stinks that I'd take the hit for it just because I'm trying to follow the rules, you know?  Oh well!

Other than the PM requirement for text books, there doesn't appear to any help doc regarding no PM response from the requestor. You might consider using the Contact Us link at the bottom of the page to contact  PBS.  In my experience you will receive a response in about a day. That said, perhaps a more seasoned member will post more helpful info. 

I always try to choose the will mail later option when I know I'm going to send a PM about a book's condition.   You can also word the PM that you will be sending it if you don't hear from them by such a time. 

You can also word the PM that you will be sending it if you don't hear from them by such a time.

This is a really good point. You have done your part, followed the letter of the rules and PMd them. They haven't responded - IMO I think you should mail the book by the time you were supposed to, again following the PBS rules. but to be safe, PM the requestor again saying that you didn't hear back so you will be mailing the book by whatever date. If they mark it RWAP, you will have the PMs to prove you did what you were supposed to do. Of course, contacting TPTB is also a good idea.

IMHO if the requestor does not respond to the PM then you can't send the book because it would be a violation of the rules.  The rules state that you must PM the requestor, and they must agree to accept the book in the described condition.  They haven't agreed so you can't send it.  It's tough for you, because you lose your spot in the FIFO, but it's better than sending it, getting it marked RWAP and possibly losing the book and a credit.

I get livehelp questions about this a lot actually.  This is what I advise (based on what I would do, not necessarily any official guidance from TPTB). 

PM the person a second time and let them know about the highlighting, and tell them if they do not respond by (XX date and time), you will cancel the request.  If they respond, great.  If not, cancel and repost.  Chances are, your book will go back to the same exact person again.  It is at that point that I would suggest emailing PBS and asking them to get you out of the loop with this person due to their failure to respond to your PMs.