Take food as an example. With the recent china soybean tariffs the way that some manufactures got around it was first shipping the goods to Thailand.
From there it is either processed or re-exported.
https://www.scbeic.com/th/detail/product/4730
So long as the middleman country/countries have lax regulations and the actors aren't pushing heavily on them, then goods can flow (all be it at increased cost due to additional shipping/repackaging).
Yeah, except people have tried to do this with aluminum by bringing it through Mexico and it doesnt' really work. This is partly why say 8517700000 from Vietnam like in my example is potentially subject to anti-dumping as if it were from China.
https://fortune.com/2016/09/09/chinese-aluminum-giant-is-tie...
Sure, it works for some handbags or sunglasses, even a few cargo containers of product, but any meaningful amount and forget about it.
Duties are based on the country of origin, a middleman country would have to do something substantial to the goods to change the country of origin (for example taking wafers and manufacturing them into bare printed circuit boards).
Even with a country doing something significant they could still be subject to counterveiling and/or anti-dumping duties for another country. For example the tariff 8517700000 which is frequently used for parts of mobile phones like the screen/keypad/bezel/antenna from say Vietnam are still potentially subject to ADD/CVD for China. Or photo-voltaic cells/panels universally flag as potentially subject to ADD/CVD regardless of the declared country of origin.
In examples like the above two part of the scope of the investigation involves companies in those countries known to use things from CN, such as aluminum extrusions for the 8517700000, that are subject to ADD/CVD so they have to disclaim it on a case by case basis or pay the ADD/CVD charges.
Source: this is what I do for a living and the 8517700000 VN example is actually from this morning with some mobile phone displays.