Always remember ( speaking specifically on spark plugs)- it takes machines such as cold formers, punch presses, robotic welding and ceramic casting ability to "make" counterfeit plugs.
These are not found at the local flea market, require immense power requirements and wouldn't fit in a good sized house and make enough noise to wake the dead.
These are not done in somebody's back room with nobody knowing about it by 2 people at night. It takes a complete factory with equipment, maintenance, suppliers and employees- not to mention the engineering, controls logic etc ( hard to hide all that in a closet)
Many of the same facilities who make the genuine article also make the less than genuine article- don't ever forget that.
Some are legitimate defects from discards but not all.
Just so you know