Now, let us consider these fundamental supply base issues as they would pertain to bidirectional supply chains. For two-level bidirectional supply chains, the manufacturing supply base issues apply with regard to service suppliers. The service firm decides whether to employ the service supplier, or whether to complete the service itself. Photographers might choose to procure the equipment to develop film in-house. Doctors offices might choose to establish their own in-house laboratory for doing blood analysis. If the service firm decides to outsource, they then decide whether to employ many or few suppliers, although the logistics of getting customer inputs to the service supplier generally favors having one or a few service suppliers. Finally, the service firm needs to select the supplier based on relevant criteria. The consideration of service suppliers in two-level bidirectional supply chains is not markedly different from the decision processesfor manufacturers.
What is more interesting is the relevance of the supply base issues with regard to customer-supplier duality. In the presence of customer-supplier duality there is usually not an option of make versus buy, since the service provider must ``outsource'' customer inputs which must come from customer-suppliers. Since customer-provided inputs are central to the service, they cannotusually be produced in-house bythe service provider.
The choice of many versus few customer-suppliers will almost always favor ``many,'' since more customer-suppliers means more customers. Supply base reduction is usually undesirable because it would limit the number of customers and the amount of revenue. Finally, supplier selection is usually not an issue under customer-supplier duality, since it is the customers who choose to be input suppliers to the service provider, not the service provider who chooses the customers.