My biggest grief with Amazon is that they now typically drop your purchases in the mailbox instead of using UPS and they often get ‘lost’.
In the 16 years or so, I’ve had maybe two Amazons get lost in transit.
Had that happen with a fairly expensive piece of electronic equipment. Emailed Amazon. They simply sent another. No muss, no fuss.
I've never had an Amazon order get lost.
In my neck of the woods, USPS and UPS are interchangeable. Which one delivers to the house is random, regardless of what is indicated online or on the package.
They have their own Amazon Delivery Trucks too.