Let me preface this by saying I am an Industrial Engineer ( a degree that combines a mechanical engineering degree with a business degree and since computers were new to industry when I got my degree using a slide rule they added computer programming as a requirement.
I learned about stamping and drawing process and die design. I also worked for a company (UL) that sent me around the world to supervise manufacturing (since by then there were no manufacturing in the US of electronic devices). I learned about how honest and forthright the Chinese are when it comes to making money. This is significant because I also had a garage that specialized in engine building and making race cars for those that had money, but no time; or just money and no interest in doing it themselves. My employees all worked as line techs at the local Chevrolet dealerships (there were three dealerships that offered me their trained techs because they paid flat rate). Because of this I spent time with them waiting for them to get off work after I had already gotten off from my "day" job.
When Chevy stopped making parts for Muscle cars (federal law requires that parts be maintained in inventory for at least seven years after that model was last sold) two things happened. First, Chevy sold their dies and licensed Brazil to make car parts for Chevys. These parts were identical to those made earlier in Detroit with one exception. As demand fell for '55 car fenders the dies were not maintained and parts stopped fitting, and price for those parts fell with lack of demand (you don't put new fenders on a '55 stock car racers destined for a demolition derby). Second thing that happened is a couple of guys realized that there were no more Chevy parts being made for their cars and bought up ALL of the NOS stock parts off of the shelves of every Chevy dealership in the US for pennies on the dollar (what they didn't buy up was actually thrown into the scrap bin where I used to dumpster dive for those parts). These guys started their business as Year One. They have long burnt through their NOS stock purchases and started buying from China along with OEM, NPD, and all of the other companies that sell restoration parts.
Those dies were eventually sold to Indonesia and China because they were the only places that still had presses large enough o hold the dies. China was converting rice farmers whose skill set included herding water buffalo and weaving grass into heavy industry. Today China makes all of the restoration parts that we weld into our cars. They are made by five companies (all owned by the Communist Chinese Government so essentially the same company). Like I said I have been there and seen the quality of their work first hand. I also know that they are very flexible with rules and safety when it comes to making money which is why UL dispatches inspectors to check up on them.
Quality: it is the luck of the draw. Quite literally. The factories sell firsts and seconds in the same box. To them a part is a part and is worth the same amount of money. You are the QC team that checks to see if a part fits or not. If it doesn't the retailer you bought from has a generous return policy. You pay to ship the bad part back and they will sell you another part drawn from the same production run (who knows you might be able to fill an inside straight with your next card from the deck).