I have never met a pilot in China, that knows a pilot in China, working for GPS. If there are any it might be Hainan Airlines, as until recently no reputable agency was recruiting for them.
There are dozens of scam Chinese recruiting agencies, most of which have zero clients under contract.
For the most part you will get one shot at working in China. If you screw it up, you may never get another chance. If your agency, with zero experience, screws it up, you also won't ever get another chance.
I would recommend choosing your agency and airline very very carefully. For agencies I would only recommend Parc or Wasinc.
I think Xiamen is a decent airline to work for. Maybe one of the better ones. Xiamen is one of the best places to live in China, if not the best. This last opinion came from every expat that I have met that lives in Xiamen. All of them like it there.