Some advice, please:

I found a good deal in the BB (with someone I've ordered from before) and placed another order.  I haven't recieved the books, but got a PM from the sender today asking me to mark them as received.  She provided the confirmation number which shows it was delivered to my city a week ago, but I haven't received any packages.   I don't doubt she sent the books, and I can clearly see on the USPS website that they were delivered (to my city), but I haven't received them/anything.

Not to sound too paranoid/accusatory, but we do have homes being constructed accross/next to us, so anyone could see a package being delivered, but we also work from home off/on so it's very common for those same people to see us in and out of our home all day (i.e. they can't always be sure if we're home or not).  We also receive packages once every ~2 weeks and have never had issues with stolen packages from our entryway.

It was multiple books for 2 credits - should I tell her I haven't received anything and mark one mailed and leave the other to time out?   Mark both as recieved?  Let both time out as lost in mail?

I want to be fair to her (she runs good deals and I would probably order from her again), but at the same time, I paid two credits and don't have any books to show for it... :-(

What should I do?

You shouldn't mark anything received until you have actually received it.  If she used PBS DC then she already has her credit.  I would just PM her and let her know that while the scan shows it is in your city, it hasn't arrived at your house.

Don't mark it until you received it.  If she used PBS DC, then she has a credit guarantee.  You can ask your mail carrier or call the post office.  Giving them the DC number will help them search for it.

The fact that it is two books makes it probably media mail.  The post office has a lot of leeway in how soon they get them to you.

You can PM her and tell her it looks like it reached your town, but has not yet been delivered.  Reassure her that you know how to mark it received from the transaction archive if it gets delivered after it goes "lost".

Yes, don't mark them received. Just PM her back and explain that you did not, in fact, receive your package.

You will get your credits back when the books get marked lost in the mail, as you should if the books are actually never delivered.

If you think that theft might be a new or ongoing problem, though, you should probably talk to your PO about options.

I checked and while she used DC, it wasn't through PBS, unfortunately, so no credit guarantee for her.

Would the PO mark it as delivered if they still had it in their possession?  Per their website:

Service(s): Delivery Confirmation^?
Status: Delivered
Your item was delivered at 10:57 am on August 31, 2010 in XXXXX, TX 75xxx

I called the general PO hotline and filed a claim.  (Local PO phone number just has a busy signal...). 

Yes.  Some POs do mark them delivered when they are given to the carrier rather than when they are actually delivered.  Depends on how many scanners that area PO has and what the local policy is.

(Some POs have scanners for each mail carrier.  Some have just a few that are kept at the PO.  Some carriers don't carry the old style heavy scanner when walking the route.  Some don't scan well.  It varies widely.)

Thank you, Emily - that makes the most sense and makes me feel so much better! 

Our mail is delivered by a guy wearing jean/t-shirts and driving a red pickup.  I can well imagine he doesn't have a scanner with him.   I was told by someone that we are considered "rural" and so they have different regulations about uniforms/transportation.    Hard to believe since we are the definition of suburbia and have a population of over 75,000...

We are also consider 'rural' Hummer, and my DC are scanned 'delivered' at my mailbox.  As already mentioned, some Postal brances use "Arrival at Unit" and "Delivered" interchangably.

Hope your books arrive!