As to the Chinese partners , yes, most of the American firms have parter firms in China, while as you said , the partner cost will be increased much especially, because both of them are growing at the same time , so the American firms will turn to the new parters, that's why they will get so many introduction emails every day. Hope this comments would help all to understanding Chinese factories and try your best to be patience to commuction with them , then you will found you get exceed your expection.

If you are a seller, do you know what are the customer's mostly concern aspects on selecting an plastic injection molding maker in China? If you are a buyer, how do you select a reliable mold maker in China?

I think there are a few good points here. One thing to keep in mind is what is the GOAL. How much material could you save by having a hot runner to each part? Is it worth the expense of the hot runner? Will you actually save that much money by using a hot runner? Another thing to consider is hot runners will typically vary more during production. There are simply more things to go wrong with hot runners(more variables to account for). Cold runners are simple and will not change. Another thing to consider is the rheological factors. By using a hot runner you might find that higher shearing laminates will bias one portion of the part over another portion of the part and this could possibly differ from one cavity to the next. Of course this could all depend on the configuration. You can reduce a few of these variables by going to a hybrid system or a hot - to - cold. But once again I would say everything depends on what is the final GOAL. If there is not much to lose by creating some scrap/regrind.... I would say Hot - to - Cold or Full Cold runner. If you have a concern of cost of scrap/regrind and the part does not call for absolute precision then maybe a full hot system. Just be sure to concentrate once again on what is the GOAL.

A lot of good points have been brought up but there is a lot of key information missing to properly answer the question. I'm personally a fan of hot runner molds, especially in multicavity tools in the right application. There are a lot of things that need to be considered up front though. The resin that the part is being molded from has to be considered, production quantity (assume it's high as you're considering 4 cavities), program life, color changes, staff familiarity with hot runner systems, etc... And as Kevin stated we need to know what the goal is to give you some more solid advise.