I need some help on how to proceed.

I got a request for a book on my bookshelf, of which there a few other copies in the system.  My copy is in Postable condition, but it has wavy pages from cheap paper.  After I agreed to mail it, I PMed the requester and explained the wavy page issue.  She was sweet about it &  wants to try for a different copy from someone else's shelf.  So, how to we cancel this order so that I stay at #1 and she can move to another copy? 

You'll either have to contact PBS, or if you haven't printed the label yet, you can have her cancel. Then, she'll need to put an RC of some sort in place that you can say your book doesn't meet, and then her request will move on to the next person.

Generally though, I'd say she's not likely to get a much better copy from someone else. Usually, the same books printed with the same paper don't vary much in quality. At least, not in my experience.

THX, Tiffane!  I thought that's what we'd have to do, process-wise.  And as for your experience that all of  the books will likely be the same, that is something she and I hadn't thought of, so I will PM her once more!