Does anyone know if it's possible when printing a mailing label from PBS to have it NOT print either First Class or Media Mail??  It seems like every time I go to the post office they tell me that I should send it a different way than what is printed on the label; if it prints Media Mail on the label they often tell me it's cheaper to go First Class and visa-versa.  I often send more than one book to the same person so the postage price is usually wrong too.

No, you can't make the class of service indicator go away without some gyrations like editing a PDF file or using an image edit program to remove the words.

You can make the correct class of service print on your wrapper by weighing your book before you print and then entering the correct weight. If your package weighs less than 7 oz, then First Class is cheaper. If your package weighs 7 oz or more, then Media Mail is cheaper. Some people go ahead and use First Class for books up to 8 oz,  because a package between 7 oz and 8 oz is only 3 cents more than Media Mail.

PBS frequently has the weight wrong on books. So that is part of the problem. If I have a book I know will go 1st class for cheaper or only slightly more than I just cover up the media mail with marker or a sticker or something. THen write 1st class on it or have the clerk stamp it 1st class.

It will not let you select 1st class for the printed postage if the book is over 7oz even though it's only slightly more. 

The best thing to do is weigh the package and enter the correct weight when printing the wrapper.

I use to be irritated by this also to the point that I finally bought a digital postal scale.  Saves lots of headaches.