Perhaps you could keep all your reciepts, and ask to see the manager and discuss what's been happening?

That's never happened to me. I have had postmasters who attempted to press my letter down so it'll fit through the slot and he wouldn't have to charge me for something oversized, and others who just slap on that fee without trying to helpful. That's about it.

OK I'm not sure if post offices' prices vary in different states/cities, but it seems every time I go to the post office I get hit with some random fee they've never charged me for before. Every time, I send the same thing: 8 x 10 envelope with my photo/index card/whatever inside, and a letter and SASE. They all weigh exactly the same amount, so weight is not the problem. But once I got charged a dollar extra for leaving the metal clip on the envelope, and last time I got charged like 60 cents because I wrote Do Not Bend on the back of the envelope. I have done both of these every time and there's never been a problem. And I've done it since and no one's said anything. There are only a handful of people working there, and how much I pay to mail the same thing depends on which person I get. Does any one else have this problem?