They didn't fine me, only made me pay the difference between shipping Media Mail vs. Parcel Post. It really irritated me, because I've given the PO thousands of dollars in business over the years...
To make things even more interesting, I knew which postal "jerk-clerk" gave me the run-around. This guy hassled me about the big box of mags when I sent them out. He's like "you're sure these are books?" I'm like "ya..." Thinking to myself "what is it to you anyway?".. When I went back to the same post office to pay the difference and get the mags shipped out (AGAIN..), I happened to get this guy again and right away when he saw me, the look of guilt on his face was obvious. He knew I was quite annoyed and knew that I knew that, he was the one that opened the box to inspect it... Needless to say, I haven't been back to the post office in some months now. It really turned me off to the idea of selling stuff for the time being.
An Ebay user also screwed me over around that time. Some lady won a top loader NES from me, filed a claim against me saying it was broken, so I had to give her money back and the *female dog* sent it back to me in a box FULL of FINELY shredded paper, making a huge mess for me. And guess what, the Top Loader still worked perfectly just like I stated in the auction.