What is the difference between evaluating suppliers of critical material in Section 7.1, and the supplier approval evaluation discussed in Section 7.3? Does Section 7.3 pertain to all materials or just critical materials?

Section 7.3 regarding sampling and testing of incoming materials is pertinent to all materials. Section 7.1 says that you should have a system for evaluating the suppliers of critical materials. Section 7.3 describes what that system should include.