A very interesting article on something that I have been noticing for years in my industry - Chinese factories subtly modifying each successive shipment with lower quality materials or specifications. It has a name: Quality Fade". http://knowledge.wharton.upenn.edu/article/quality-fade-chinas-great-business-challenge/
From my limited experience it is rampant. The best thing to do is tell them your not buying any more & will deal with another company because of the quality issues & suddenly it will turn back around . Usually they will test you to see if you accept it with no recourse & rectify it pretty swiftly when you contact them about it offering a discount on your next order .The price of return shipping usually isnt worth it so negotiating a discount or extra stock on your next order is the only feasible option
It can be very dangerous buying from the Chinese. You can end up with something different from what was agreed, and then you're selling something that doesn't meet safety or govt performance regulations.
