There are a lot of life safety devices which are made by someone other than an end user, after competitive bidding.

You either need to do testing of every article delivered, or set up something like ISO 9000/9001 quality management and accept that you will be paying a premium for a documented, repeatable process.

Counterfeit parts getting into the supply chain (which might be visually identical, and may even appear identical to testing) are a problem, but that's where having documented/audited suppliers comes in.