It's not that I trust them, I just trust them more than a guy (not you) who wings it and thinks he knows the best way to fix it when that way contradicts the OE repair procedures. If I were king, those parts would be available to anyone with the knowledge and equipment to fix the vehicle per OE repair procedures, but that's not how it works. I suspect that, in part, the OE wants plausible deniability when a repair shop fixes a vehicle in a manner that deviates from the OE repair procedure by being able to say that they limited access of the necessary parts to those shops that they knew to be qualified.