I submitted a Box of Books request to someone I had dealt with in the past this morning, suggesting a swap of 4 for 4. .  Call her Member 1.  She responded quickly with 4 books.  I was going to hit accept but I wanted to make sure I could find the books.  When I came back to the site this afternoon, someone else (Member 2) had requested one of the books that Member 1 had requested on her BoB list, and the book was removed from the BoB list leaving 3 there.

Now I would really prefer to send the book to Member 1 because she did ask first and I prefer BoB because my thrifty soul would rather mail 4 books at a time than 1.

Would it be ok to tell Member 2 that the book is not available and have member 1 put it back on her list or is this even possible with the setup of the site.

I've rejected requests that come through the non-BOB system while I have a pending BoB with that book on it.  I typically say "sorry, but this book is currently in a pending box o books"

Yes, send it with the BoB. When you cancel the request, the book will be removed from your shelf and the request will be passed on to the next person who posted the book. You'll have to repost it to put it back in the BoB.

The only problem would be if you have the only copy of the book. When you cancel, the requestor will go on the wish list and when you repost, it will be offered to him instead of being available for your BoB trade.

Or you could just cancel the trade (removing it from your BoB list), accept the BoB as it is, and send a PM to the BoBer saying "I just wanted to let you know I will be including book LLL in your box, as originally set up.  It was requested before I could accept the BoB--I've declined that request and will put it in your box, but am not reposting it so it doesn't get requested again before we can both accept."