It would be helpful if any new supplier you chose was certified to ISO9001 or ISO/TS 16949 but in reality many small suppliers won't be. When you are a low volume manufacturer your options become squeezed. For any safety critical system you need to make sure the parts you are fitting are always up to the job. Quality audits compare a range of criteria against defined information, either published standards or an internal quality manual. In some instances bad procedures can't easily be identified without a good technical understanding.
Engineering Inspiration can support your quality engineer to audit a suppplier and give guidance on critical technical concerns.