Today, someone requested the same book twice. First they requested it, then canceled the request, then requested it again, then canceled it again. They also PM'd me to say that they already had the book, but were looking for a couple of summary cards that came with it (it's an audiobook). Their last PM (just before they canceled the book for the second time), said that they were going to cancel the request if I didn't respond within two hours (yeah, like I spend the whole day at this site, waiting for requests and PMs!)

I don't understand this person at all. Is there a way to block individuals from requesting your books? I would be really leery of sending this person anything, because their demands are so off-the-wall.

The requester might benefit from the use of a specific Requester Condition explaining what it is they're after.  If they were to leave those conditions on, you could decline and the request could move on to the next copy in line.  When ordering any other titles, all they would have to do is turn off the RC just before placing said orders, then turning them back on in case their conditions for this particular audiobook were declined and passed on to another member.  You might want to send a polite message to that effect, then if the order came through again you could decline the conditions and move on.  I don't think looking for all the accompanying material qualifies such conditions as "off the wall", but I think the fact that the member is trying to complete a transaction as such without the aid of Requester Conditions is less sensible than making use of the tools PBS provides for precisely these purposes.  People are often leery of certain conditions (or, for some, Requester Conditions in general), and were this member to use RCs then you'd have every right to decline, without anyone becoming any weirder than they'd like to be :)

What Jimi said -- Wanting the extra material for an audio book is a bit like wanting the dust jacket on a hardcover.  A requestor condition would solve the problem neatly.

It's not the request for the extra material that bothers me--it's the fact that the requestor kept requesting and canceling the same item over and over. It's also annoying that they expect me to be online all day to answer their PMs.

Sounds annoying Erica, but not worth your time.  As mentioned above, you might send the requester a polite pm that they may find an RC helpful.  Then make a note of the name and ignore this member.

It sounds like maybe they are impatient to get the book sent to them immediately and they don't understand that when they cancel the request then rerequest that it goes straight back to the same person it had gone to before. Maybe you could explain that to them and see if it helps. Or you could ask a tour guide or pbs to do it if you aren't comfortable letting them know.

I'll send the person a PM, though I think they may not understand quite how PBS works. Here is the last PM they sent me:

I f you don't respond in 2 hours, I will cancel, as I have a need to get something quick for today.
Not to alarm you, but I just wanted to be clear.
 

There is very little chance that any book will go from the sender to the receiver on the same day. Also, this request was made Sunday, when there is no mail service in most towns.

Also, even if they cancel and re-request, the request is coming right back to you, because as soon as they cancel, your book goes back to the front of the line to be requested next.