It doesn't matter. If it's a textbook^* then you have to get permission from the requester to send a book with underlining. If it's not a textbook, then you are not allowed to send a book with underlining. Since your book doesn't have underlining, you can accept the request and send the book.

^*PBS has said in the past that pretty much any book could be used as a textbook in some class, so really all books have to meet the textbook rules and you can send any book with underlining as long as the recipient agrees.

okay. thanks Cathy for the great answer.

Basically the RC is requesting a postable book. Per PBS swappability rules, books may not have any writing, underlining, or highlighting on text pages.  The only exception would be books posted under the Textbook Waiver, in which case there is a specific guideline that must be followed.

I tend to turn down any vague, confusing, or excessively long RC's.  But if the book is postable, I would not hesitate to accept and send this one.