How does the layman consumer inspect/assess the quality/safety of other drugs or really any other substance that they ingest?

That's a fair question - they obviously can't inspect pharmaceutical factories. That said, the FDA has much more power to regulate drug manufacturers than pharmacists and most drugs are manufactured in a few locations that are much easier to inspect. They only have to make sure one or two locations are set up correctly and a significant chunk of the application for clinical trials is quality control procedures.