Almost a week ago I got a notice that a book I shipped was lost in the mail.

However, I emailed the receiver asking them to confirm that the book was NOT received.

I haven't heard back from the receiver.  Maybe they are away???  Tomorrow will be one week since my email.  Should I wait a while???

If he/she has a profile - check to see if he/she is still a member.  If not, I'd contact R&R and ask for your credit back.  I'd wait exactly one week before PMing the member again.

Check out the Help Center ~ write "lost book" in search engine under "Browse Help Docs".  That will give you the procedure you should follow when this happens.  You may of course be right, the requestor may be away and was not there to mark the book received when it came.  If they go to their Transaction Archive they can mark the book received from there and you will receive your credit that way.  If however you don't hear anything in a few days time, send feedback to R&R and they can find out what is happening with that persons account, on hold, whatever.