How do I invoice a customer in country A and deliver the goods to another customer in country B? Any ideas?

what is the issue that concerns you? this sounds like standard behaviour

I am wondering if adding the second customer adress on the first customer card is the way to do it?

Oh I see now. I think it depends on what you want to see. How much flexibility do you want to have? Do you want to manage assets that you shipped to B but remain owned by A. or Is it like a performing a dropship? What documentations will be needed? Many factors can play. At the base level is an SO to Cust A, manually enter Cust B as the "Ship To" and then an Invoice/Commercial Invoice. Will A want you disclosing the prices to B?

I understand the complexity of the question. And I want to get the tax code correct. Given I am in the EU, I want to make sure we can support both internal EU trade and non-EU exporting. Country A will invoice country B while country C will receive the goods. All three are different parties (triangulation trade). I guess we will go with the simplest way to add several adressess to the customer which will receive the bill. Basically change the "ship to" as you are saying to customer B on customer A.

Check this SA https://netsuite.custhelp.com/app/answers/detail/a_id/44830

Yup, saw this earlier. Sorts the EU triangulation reporting. For non-EU exports, it will simply be a SO with a export outside of EU tax code added with different ship to bill to.. should be right I hope.