If Amazon has its own warehouse and unified delivery, it is impossible to choose a courier company during the purchase process.
The delivery time is unstable. You can select the arrival time before and after the payment ends in the interface. For example, if you want to deliver the goods the next day, you need to pay high freight. Like saving freight, you can choose 4 to 8 days to arrive, and the freight will be relatively reasonable. After reaching a certain quantity, the freight can be exempted, but the delivery time is very long (about 8 to 15 days).
In addition to Amazon, there is also an online shopping company in the United States, EBAY. But on a smaller scale than Amazon. Their delivery method is very interesting-through the post office. Due to the dispersion of American houses, the difficulty and labor intensity of delivery are relatively large. Ebay usually entrusts the post office to deliver the courier for them. There are also Amazon products bought on ebay and delivered to your door by Amazon.