Overhauling the front suspension of my vehicle requires having just about 2 of all parts. I spent many hours and trips back to the store to get two of the same drive shafts, two of the same ball joints and the correct brake pads.
Typically the store only kept one of the parts and each time the other part would be delivered to the store (with the same part number) there would be inconsistencies between the matching parts. This resulted in waiting another day for the next shipment, or going to another store to physically see the part they had in stock so that I could obtain a matched set
The ball joint issue was the worst. Collected the first pair at another store to find (after getting home) that they were completely different designs. Exchanged the item that would not fit for another that looked the same in the plastic packet (at least it had the same box) only to find that on assembly it was a different size. This required searching the local stored to find a match for the one already installed. Two days wasted on that little item alone.
The bad part of this is that the store keepers had no concern about my problems, they also had no issue returning/swapping parts that just went straight back to the shelf for the next guy to worry about.
My conclusion is that the parts, made in China, are obtained from various factories. There is no consistency in the supply chain.
There is no process to eliminate bad parts they simply rotate them from store to store as needed.
The scenario is probably much, much worse if you start using 're manufactured' parts.
Lesson learned: buy from the dealer, it may cost 20-30% more but the frustration level is worth it even though I spent over $1200 in inferior parts.
Now I wait for those 'Lifetime' guarantees to kick in, I am dreading the moment. Probably just buy a new car to avoid the frustration.