Competition for capacity and skills is on the increase in China and I suspect that some manufacturers may be sub-contracting some work out to newer 'start-ups' as well as firms with less than stellar quality control standards.
Diecast from companies like
GMP, Carousel 1 and
Eagles International, will definitely command a premium price due to their dedication to high quality manufacturing and quality control

.
(The June 2007 issue of
National Geographic has an interesting article on China's 'Boomtowns'.)