Been my experience that it is pot luck with car parts. The name brands such as Dyna Corps, NDP, and the more expensive retailers get their parts from the same source in China as every one else.
Difference is they have a knowledgeable buyer working in China that inspects what they buy before it ships for fit and quality. The rest like I say is pot luck.
This isn't to imply that these guys use a QC program like GM did at their factory doors back in the sixties and seventies inspecting all of their parts with calipers and micrometers and rejecting everything ordered if the percentage of bad parts got over 2.5% of the lot.
They just throw back the obvious defects before trying to sell it to their customers and check others with go no go gauges. This is because the factories in China ship everything: drops, seconds, blems, all in with their order in the hopes that nobody will pay to ship it back.
They all have a money back gaurentee provided you dont bend it cut it or scratch it while trying to get it to fit. You are in effect their quality assurance and check for bad parts for them. They usually have a large selection of returned parts on the cheap that they don't want to pay to ship back to China that they sell on the cheap With no gaurentee on offer.
Big Dave