i sent someone a book and they have not marked it received. it is not past the date when PBS will consider it lost. could i send them a PM asking if they got it but did not mark it received or just leave it alone? other books i sent after that one were marked received long ago. thanks!

PBS sends out two reminders.  One a week before the lost date.  Another right about on the date.  So there is a risk of alienating a member who has not actually received the book.  I do look to see how long they have been a member and when their last book was posted.  Just to get an idea how active a member they are.  Then I wait. 

I will sometimes send out a PM when a book I ordered is about to go lost.  Something along the line that the book has not arrived and that I know how to mark a lost book received.

I never contact anyone.  I don't even really pay attention to them once I mail them.  Only 1 had ever gone lost. 

I did that this week on a book that was due to go missing on Sunday. I sent them a PM and they replied that they got it and forgot to mark it received. As long as you are polite, it is fine to ask, but I would wait until a week or less before the "lost" date. I wouldn't say "did you get it" but something like "hopefully it shows up soon" or something similar.

I always wait until about 3 or 4 days before the book will be marked lost in the mail. Then I send a polite PM, something along the lines of

"Hi, I was checking my account and I see that "Title of Book" is about to be marked lost in the mail. I was wondering if you have received it yet? If not, I would like you to know that I mailed it on time, so hopefully it should be arriving any day now. Please let me know either way, an answer would be appreciated! Thanks!"

Out of the 6 or so books that I have had to send a PM about, 5 of them were marked received within the day. Usually with some type of apology in a PM.

Like Sara, I'll wait till just a few days before the lost date.  I also take location and weather into account.  If the package was traveling across the state with no weather extremes, I might pm a few days early.  To the opposite coast with weather (ie Sandy or other storms), all the timeallowance for sure.

Sending a PM a few days before letting them know the book was in fact mailed is fine. Sending a PM any earlier than that or doing so to ask if they have it will come across to them as accusing them of some wrongdoing because if they had it - then they'd have marked it received right? They system handles the reminder emails. You can send a PM just before it goes lost that will let them know you know they haven't marked it received, but it is usually better to word it in a manner that doesn't question their honesty.

"...word it in a manner that doesn't question their honesty."  

On the rare times it's happened, I've usually just let it go lost. I figure they get messages from PBS and that's good enough. 

I'm with Sarah and Heather. Once or twice I've been glad I sent my super non-judgmental message as the person discovered her building complex management company was holding it hostage and she had to go hunt it down. This also has happened when I've sent a book to a University dorm - it got stuck in their private mail system. So, I think sometimes a "did you get the package okay" message is fine to send a few days before it goes lost.

I almost always use PBS postage (whatever that's called), so get instant credit, but do watch the books in transit (because it's so interesting to see how books get from Point A to Point B).  If I notice that a book has been marked delivered by USPS but not received by the requestor for a few days I'll send a PM saying, "Hi, I noticed that USPS marked the book I sent as delivered on [insert date].  Just wanted to make sure you got it.  If not, I'll be happy to ask USPS to start an invesigation.'

I've probably done that three or four times and the books are invariably marked "received" within hours.