Customs inspection in the airport was not a problem to me also when carrying small quantities of gold and silver coins.
Other than auction houses that are not exporting coins I could not find even one shipping company that is willing to ship coins out of the mainland. I contacted quite a few and always received the same answer that they do not ship coins. This is where my confusion was as to what the exporting regulations really are. If anyone knows a shipping company that will do so please let me\us know.
If those shipping companies don't ship coins who does? Because the China based eBay coin sellers don't seem to have any problems shipping coins overseas. They use what they call "eBay mail" which I think is just a regular parcel shipping postal service with a transit time of about 2-3 weeks. They usually declare the items on the shipping label with an amount that makes everyone happy and does not generate any import levies. I request for a faster shipping service such as the EMS Speedpost or the AAA Express when I buy more expensive items; they get to me in the USA within 1-2 weeks. No package has gone missing except for one that spent months in transit and was eventually returned intact to the seller.
If I was to buy coins when visiting China I'll probably have them ship any items I do not want to carry with me. Previous posts identified locations of some of our well known eBay sellers in China. I could aggregate my items with them; they have expertise and the connections to do it seamlessly.
Best wishes and good luck.