What are the easy ways to arrest the defects of the parts ?(by quality inspector)

Firstly you hv not mentioned the part u want to inspect. Anyway in general if you want to arrest the defects in parts then first you hv to check its design (mechanical/electrical) visual. 

1. Visual Inspection

2. Quality Check (Testing functional)

3. If new product do type test as well as functional test.

the testing process depends on the product u r using. And remember the standards(Local and International) used while manufacturing. In those standards' documents u will get the testing process designed by experts.