Respectfully, you might want to revisit that assumption.
From what I’ve seen, it’s more likely they just test one vial from one of the kits they buy from CN, then re-sell individual vials from every other kit they buy.
I just bought a single vial from a US vendor who coincidently experienced the same delays as vendors from CN, then sent me a vial with a QR code corresponding to a test for vials with completely different colored caps.
In other words, they did not test any samples from the batch my vial came from.
A better heuristic might be that since they’re in the US, the vendor might fear getting raided by a regulator, and that fear might make them more likely to be careful in some way. But then again we’re talking about ppl who are willing to risk making someone sick by selling unregulated injectibles.
I’m not saying don’t take a risk - clearly I take mine. I’m suggesting there might be room to make your risk assessment even more robust. This site’s an invaluable tool for helping with that.