While waiting to drop off a box of books, there was a guy picking up 3 large produce boxes that were shipped to him using media mail.  The PO opened them and deemed them not to be media mail and was charging him an additional $55.  He had them open one of them (to prove his point that there was only paper in them).  Surprise, there was a t-shirt and jeans stuffed in the middle of loose leaf binders, folders, etc.  He claimed this was "stuffing material" to keep the paper from moving around.   20 minutes later as I was leaving the building the guy was still arguing with the clerk. 

The clerk was great - I'm not sure I would have been on the other side.  Kudos to those that have to work behind the counter. 

At that point, I think I would have refused the shipment and have the post office return it to the sender.  Then I would chew out the sender something mean.