Final answer:
The concept in question is excludability in a trade or business, which is crucial in international trade and capital movements. The examples illustrate how services can be selectively provided to paying customers only, and the difficulties in restricting international financial flows due to economic interdependence.
Step-by-step explanation:
The question appears to revolve around the issue of excludability in the context of a trade or business where both personal services and capital are significant factors for generating income. Excludability refers to the capacity of a service provider to prevent those who do not pay from using its services. In the examples provided, primary education and cell phone service are cited as excludable because providers can prevent access to non-paying individuals.
Further, considering the reference to international financial flows and the challenges associated with restricting them, the discussion involves international trade and capital movements. The difficulty arises because national governments can only impose taxes within their jurisdictions, and in a global economy, financial flows are hard to restrict without affecting legitimate trade-related payments. This highlights the complex interdependence of trade and financial capital in the international economy.