My local post office has a bad reputation because it is completely understaffed, but the people who do work there, when they aren't cranky due to cranky customers, are actually quite nice and helpful. I used to think UPS and FedEx were good companies with good customer service - and probably the used to be! - but most of my non-simple interactions with them over the past few years have been pretty horrible. Managers do what managers know how to do...
piss off their workers.
