At our local PO here, especially around the holidays, they open a separate counter out in the middle of the floor with several postal carts to toss incoming packages into. They put a person at that counter who simply accepts the packages and tosses them in the appropriate bin. No scan is performed.
The counter is often unmanned throughout the day and the bins left unattended.
There is no way, period, I'd ever use that counter. There is nothing stopping any one off the street from just picking up a package and walking out the door.
NEVER leave a package without it being scanned and being handed a receipt.
Doing so may mean waiting in the longest line but its the only guarantee of proof of shipping.
I use USPS for anything up to their max standard size for items shipped somewhat locally, (east coast), if it has to go cross country I rely on Fedex.
I NEVER use UPS. I watched a driver once who had 10 or so new bikes in boxes on his truck, they didn't fit on a shelf and were laying on the floor sideways. I watched him walk back and forth over top of those new bikes in the box as he hunted for a package. The bikes were headed to a local bike shop. I personally knew the shop owner, and knew he had issues with damaged bikes, how they were getting damaged was now obvious. When I told the driver he shouldn't walk on a bike box like that he sniped back at me saying if they didn't want them damaged they shouldn't have jammed up his truck like that with big boxes.
I've also had UPS drop packages all over the place during delivery, on the front porch, side porch, at the curb, beneath my roadside mailbox, next to my garage, next to my neighbors garage, and in the front bushes along the front of the house. I even watched one guy stop and literally kick a bike box out the door onto a neighbors driveway behind a his car and drive away rather than carry it up the drive to the house. It landed behind the back wheels, in the dark. I barely caught the guy in time before he backed out and ran over the package. It turned out it wasn't even his, the address was for a similarly named street 10 miles away. UPS refused to pick the package up after he called, he finally had to deliver it to the right owner himself assuming it was likely some kids Christmas present.
The biggest issue I've had lately with USPS has been packages showing up as scanned and delivered but not having yet arrived.
I had a box show as 'delivered' last week. Yet it was not here. Two days later it showed up as being in route from the local depot to my local PO, AFTER it showed being Delivered? It showed up three days later in my mailbox with no further scans.
I've had more than 5 packages in the past year show up as delivered after 3 days, yet not show up for almost a week. I'm not sure how that can happen unless the carrier is scanning them and tossing them back in the incoming mail bin in the truck?