I dissected customer returns. Again and again, the products in later shipments looked identical on the outside, but were "cost reduced" on the inside. For example, I would see empty places on the circuit boards where the filter capacitors were supposed to go. In one batch of one product, many of the units were dead on arrival, on the ones that worked when I unpacked them, the solder joints only lasted a few weeks. Once opened, I could see that the boards were either soldered at the wrong temperature, it was the wrong type of solder, or badly made solder. Every connection was visibly a cold solder joint. Either the factory had no quality control, or they ignored the quality control.
Other products looked identical inside and out, but based on the failure rate, the factory must have gotten a bad batch of one the components.
Even longer ago, I worked on a product that logged data to a Compact Flash memory card. It was an embedded product that needed to work across a wide temperature range, including in the winter in Minnesota. The big names like SanDisk would randomly swap component suppliers. Our largest customer saw less than a 2% failure rate, but that was way too much. We found a specialty supplier that charged 5 times as much, but they had a rigorous quality control process. They paid attention to the specifications. They tracked where parts came from, and promised that we would be able to test sample units if they needed to switch suppliers. Alas, the 2% failure rate from the earlier parts had already doomed that product line.