Does anybody really know what happens to defective parts?

So I work in a independent (used to be mom and pop) automotive parts store and I got to thinking... what do the manufactures do with their defective electrical parts? like alternators, sensors, wheel bearings? Do they re test em and sell em over again or do they just throw em away and not question whats wrong with them? via /r/cars http://ift.tt/2ujAut9