美国政府实际上是如何在物理上执行进口关税的?

How does the US government actually enforce import tariffs physically and how do they collect the money?
美国政府实际上是如何在物理上执行进口关税的，他们又是如何收取这些费用的？

How? Let me use a typical shipping container as an example.
如何？让我用一个典型的集装箱作为例子。

When
cargo arrives in the US at any port it is in a controlled environment.
All ports are divided into a customs cleared part and an uncleared part
and all this is controlled by paperwork and computers.
当货物到达美国的任何港口时，它处于一个受控环境中。所有港口都分为已清关部分和未清关部分，所有这些都由文书工作和计算机控制。

When
it arrives the container number is entered into the customs system and
all the parties are notified. The shipping company gives notice to both
the importer and customs that the container is there. An “arrival
notice” or “advice note” is given to the importer.
当货物到达时，集装箱号码会被输入到海关系统，所有相关方都会收到通知。航运公司会通知进口商和海关集装箱已到达。进口商会收到一份“到货通知”或“通知单”。

The
importer or his broker match this arrival notice with the commercial
documents. The documents will be the bill of lading and commercial or
customs invoices. They then present the document package (or electronic
equivalent) to US customs along with a declaration that states the value
origin and description of the goods. The importer/broker will determine
the correct tariff number and rate of duty and the declaration will
total the duty and taxes owing.
进口商或其代理人将此到货通知与商业文件进行匹配。文件将包括提单和商业或海关发票。然后，他们将文件包（或电子等效文件）连同声明一起提交给美国海关，声明中说明了货物的价值、原产地和描述。进口商/代理人将确定正确的关税编号和税率，声明将总计应付的关税和税款。

Then
depending on the credit arrangements the importer has with US customs
they either pay the duty at that time or they receive a monthly bill.
They pay the duty to the American government.
然后，根据进口商与美国海关的信用安排，他们要么在那时支付关税，要么收到月度账单。他们将关税支付给美国政府。

Once
US customs has verified the declaration and duty amounts they will send
a release notice to the port where the container is. Only after this
notice is received will the container be allowed to leave the customs
controlled area of the port.
一旦美国海关核实了申报和关税金额，他们将向集装箱所在的港口发送放行通知。只有在收到此通知后，集装箱才被允许离开港口的海关控制区域。

The
procedure varies a little from port to port and air truck and ocean
shipments are all handled a bit differently. But the above is the basic
method.
程序因港口而异，空运和海运的处理方式也有所不同。但以上是基本方法。