Yes, the good stuff is excellent, and the crap is utter. You don't get utter crap from a supplier here.
We've ordered parts from a Chinese supplier, and found that half of them had defects. It was still cheaper than getting them from a North American supplier if we threw out half of them, so we did. Later we found a more reliable supplier and we're getting good quality parts at a great price.
A friend of mine ordered lenses from China for his business. Got a sample and it was fine. Paid for and received the production parts and they were hilariously awful. They wouldn't take them back.
We still get the vast majority of our parts made in the US and Canada, but for certain items it's far less expensive to get them from China if we can find a good supplier.
Bizarrely some North American suppliers have raised their prices 5X and basically forced us to go to China. We were sticking with them at 2X China pricing, because the extra shipping costs and hassle wasn't worth it, but at 10X China pricing it's absurd. There's no difference in quality... I think the North American supplier is just selling to customers who are buying small quantities, or can't be bothered tracking down overseas suppliers, or who think that the expensive ones are better quality (they aren't).