No, imported mattresses do not have to go through customs because they are not considered a hazardous material.
Yes, but you will most likely have to go through the same channels as firearm importers, working with whatever paperwork customs will give you.
it is very hard to go through UK customs
You go through customs when entering or leaving a country in Europe.
You go through customs when leaving the US before boarding your international flight.
Yes, customs officials may inspect your luggage during international travel to ensure compliance with import/export regulations and to prevent illegal items from entering or leaving a country.
to the airport
When leaving the US, you go through customs at the airport before boarding your international flight.
You typically go through customs when flying to Europe after you arrive at your destination airport.
When flying to Europe, you go through customs at the first airport you arrive at in the European Union.
Yes, passengers connecting through Atlanta on an international flight will need to go through customs and immigration.
Yes, passengers connecting through Dublin on an international flight typically have to go through customs and immigration.
Yes, when leaving the US, travelers typically go through customs at the airport or border crossing.