I sent a book March 2 using pbs shipping. It is no longer showing on my Books Mailed.  Today it came back with the USPS tracking number taped over.  Also someone had apparently hand written a statement that the person has moved.  Is my obligation over?  I sent it to the addressee on the PBS sheet with adequate postage paid.

But I feel guilty.........

 

Why do you feel guilty because someone else moved and didn't bother to change their address? You're under no further obligation, so no worries. Here's the official word:

It is the requestor's responsibility to provide a working address to senders.  If you do not keep your address current and correct on your account, you will need to give credits for (=mark received) any books that are sent to the wrong address, whether or not you are able to collect them, and whether or not they are returned to the sender.   Providing a dependable, correct address to senders is part of the honor system that helps keep this club working so well, and it is essential to maintaining membership.

You are lucky that you sent it with DC because otherwise it would have been returned to you postage due -- media mail does not include forwarding. If you want to pursue it further, PM the person who requested it, explain what happened and let them know that you would be happy to send it to the correct address but they would need to send you another credit to do so. But whatever, do not feel guilty -- YOU are not the one who did anything wrong!

I agree, your obligation is complete.  You may wish to notify TPTB, if the requester has not corrected their address problem PBS admin may want to put the account on hold to save other members from your situation.