I wouldn't say it's "secret," it's just regular business conducted using a language most Americans can't read or understand. Probably even in dialects that most Chinese people can't speak.

I think the fruit thing isn't "secret", but my friend's families do a lot community-wide legal and financial gymnastics to pay as little tax as possible.

If the social technology in these networks is better (produces both cheaper, better quality product) then there is money to be made copying it/adopting it.

I don't think it's so much a "secret network" as it is a community network. A strong community network is absent for a lot of Americans, so it probably seems strange or secret when they come across one.

Although for Chinese dollar is the King, they form deep communities to aid each other in trade and are loyal. One interesting example of strong communities - I have newer seen a Chinese beggar in Europe, but a lot from neighboring and other countries.

Are they particularly secret, or just filtered through social networks?