供应商审核的疑惑

Customer will come to conduct supplier audits in recent days . The contents of supplier audits are production flow and quality system, to ensure that the product of our company produced can meet their demands steadily .I am confused why we are always audited by customer but never conduct supplier audits to our suppliers . The department of testing raw material for production in our company is physical and chemical room , which is not beyond QA . For raw material , qualified products are normally received and substandard product will be received concessively after re-sampling testing pass. A-fram which is used for product packaging and transport , its main parameter often exceed specification and few on-time delivery . We have received a lot of customer complaints for that . All companies I have worked for are almost the same about supplier management . Given this facts , I doubt that quality management as well as quality system is flower in the water and moon in the mirror. Who can explain the doubt in my mind ?