It is uncomfortable for me to quiz parts suppliers about the country of origin of what they're selling. They often immediately get defensive and give me the BS that "They're all the same" which I know is not true. The parts retailers are in the same boat as the rest of us, faced with a flood of low quality crap from China and a near absence of quality parts from North America or western Europe.
The good stuff is out there, but a challenge to find.
As the customer you should never have an issue with questioning the origin of parts you are purchasing. Ever.
With the influx of poor quality parts, especially soft parts, from countries like China it gets more and more difficult to determine if you are getting a quality part. Sadly, the market has driven things to this point - for example, I recently bought a front flex disc for my 1995 S500 coupe. Here is what I found:
URO - $39
Dorman - $55
Lemforder (OEM) - $117
Mercedes - (OE) - $185
I chose the Lemforder. Had I not employed a parts supplier who knows the difference between all of these variants and also strives to get me the best deal on OEM parts, I might have ended up with a sub par part that would most certainly have lasted far shorter a time than an OE or OEM part would.
If a supplier takes exception to you questioning a part or it's origin, I would find another supplier in a hurry. The only thing to be gained by selling these lousy import parts is profit - for the seller.
For the record, I use Gary Hurst of BuyEuroParts.com
Gary knows the parts, the suppliers, and has a vast knowledge of what is good or better and why. He'll also tell you when you can save a buck and just go to the dealership. And when you call, you talk to Gary, not some brainless counter monkey who is looking at a computer screen and drives a Nissan.