Re the postal service being a job that "really doesn't require that much to get into," I don't think that is quite true. A lot of the clerks are what they call temps, even though they can work for the post office for years. They don't get benefits and they don't get the good pay. Even a lot of the rural carriers are temps. So there's that to consider if you get someone who is a crank. But sometimes people are just cranks. I too have had people who had no conception that customers like me are where the money is, not someone coming in to buy a stamp. Some people are idiots. What can you do. I myself almost never go to the actual post office, though. I mostly just deal with the carriers, and then when there is a problem, I usually contact the 800 number, because they seem to be a bit more responsive than the local office.
OTOH, I have gotten fed up with people who hate the post office and consider abolishing it to be necessary to life on this planet. To a man, they never know jack about it and rarely use it. Their objection is not based on reality but on some weird ideology. I would like them to explain to me how they think US business would be affected if the post office ceased its existence. They can't. As far as I am concerned, they have absorbed so many "talking points" they are no longer capable of reasoning. They just yell about how it's a "failure." I have used the post office for the past ten years as a fundamental part of my business. They are able to get a package from my pokey town in upstate NY to CA in ONE DAY for five dollars. That's not what I call a "failure."
I don't use UPS because I don't see any need to. Maybe I would if I sold stuff that was bulky or heavy; I don't know. I like using the online software for postal shipping (NOT the post office site, which is terribly designed). The UPS drivers are great but more and more nowadays I get boxes from UPS that are really banged up, even squashed. In contrast, this rarely happens with the post office. The UPS driver asked me if it was okay for him to ring the doorbell and just leave stuff on the patio and I said yes. He doesn't leave things in plain sight. He has some consciousness about what he is doing. The FedEx guy, in contrast, has never spoken to me and leaves brand new printers in their printer boxes in the middle of the driveway. I am lucky I am usually here and hear the truck.