I had a book that I printed PBS postage and DC on and mailed out media rate. It came back to me (never got past my own post office) *supposedly* because it was under the size/weight limit for media and needed to go first class. They are now telling me I have to pay the postage on it all over again even though the media cost was higher (and despite the fact that the book only went the 2 miles to my own post office).

Last time I had an underweight book that had to go first class, they just marked through the DC on the label with a black marker. I don't know why I'm having a problem with this current book.

There is no minimum weight or size other than the normal standards to mail something. It may be cheaper and faster to go first class but otherwise I do not see a problem. The DC cost is the same for both classes of mail. If I had the book, I might black out the M for media and send it first class. It should be able to go as is.

First Class must be 3/4 of an inch thick to qualify for DC though.  I don't know if that same rule applies to Media Mail rate to get DC on it.

The issue probably wasn't that is was undersized for media (there is no limit on that), far more likely that it was not thick enough for delivery confirmation (has to be 3/4" or thicker, with "thick" defined as the smallest dimension :-)

That rule is only for first class Bren, a thin book can go with DC via media mail no problem. If you sent it media, it should have went. They'd have it backwards if it is a thin book with DC and they wouldn't send it MM, but are asking you to send it FC, might end up with someone smarter down the road sending it back again if that's the case. Sounds like you got a PO employee that was a little mixed up with the rules. Can you ask to talk to someone who is higher up?

If they are saying it is too thin for DC, put a packing peanut or ball of paper in one corner and make sure it is 3/4" thick there.

The other option is to put stiff cardboard in the package, if it is rigid, it also qualifies for DC.

That rule is only for first class Bren, a thin book can go with DC via media mail no problem.

I don't think that is correct. 

http://www.usps.com/send/waystosendmail/extraservices/deliveryconfirmationservice.htm  says

"Note: All items (except Priority Mail) mailed with Delivery Confirmation must measure at least 3/4" at the thickest point, or be in a rigid box."

Stamps.com will not print delivery confirmation for the "large envelope" class but will for "thick envelope (over 3/4")" for either first class or media mail.

I understand the 3/4 inch rule. What I don't understand is why they didn't just black out the DC label, black out Media Mail, stamp it first class, and send it on its merry way (which is exactly what they WOULD have done if I had mailed it from the post office). I paid MORE than enough and should NOT be told I have to pay for it again, IMHO.

I would ask to talk to the supervisor. The DC should be left alone to be scanned at the delivery office. They track how many scans you should have and send nasty grams when you miss them. Returned for postage mail is not postage due. Did they charge you to get the book back? I hate these new rules that require judgement calls.

Timing is everything, I guess. I got this memo at work today....All first class parcels qualify for DC. This came from the national level USPS office. Interesting, as I have scads of memos from the local district level reminding me the opposite. This is how I thought it should be but who am I?