Do you mean "customer"? No, "customs" and "customer" are not the same. Customs is "the place at a port, airport, or border where officials check that the goods that people are bringing into a country are legal, and whether they should pay customs duties".
(French: douane; Spanish: aduana)
Customs duty would usually refer to the tax charged on imported items.
Customs would usually refer to the office or place where officials check imported items.
The phrase "he is at..." would normally refer to the place where "he" is located. In this context, customs duty does not make sense.
I think it's too vague. In many countries, customs is separate from immigration/passport control. Also, there are cutoms offices at airports. Going through customs doesn't necessarily mean that you're actually crossing a border. In Germany, the Zoll also has a few non-border-related responsibilities such as combating illicit work and money laundering. That's why there are Zoll offices all over the country.