Er Nai - 二奶 - Concubines - Green hat - Booming luxury product sales in China

What do all of these have in common? - Er Nai - 二奶 - Concubines - Green hat - A bit on the side - A bit of how's your father - Rumpy Pumpy - Booming luxury product sales in China.
To the best of my knowledge an Er Nai is a woman (mistress) who allows herself to be the mistress of a married man ( a sponsor) for personal gain.
Normally money, property or basically anything nice in the luxury product range is acceptable.
She may or may not argue she is doing it for love.
The man provides these gifts in secret (but not always) from his family, especially his wife.
This relationship can and often does, go on for years or until his desire for the Er Nai disappears or as is sometimes the case, a younger Er Nai appears on the scene.
Er Nai are mostly always young women but not always, around the age of 20-30 years old, sometimes younger.
Being an Er Nai is basically a paid job, that is one justification.
Er Nai who meet their sponsor through work will usually resign before officially becoming  his Er Nai.
They tend to be hidden away from normal life only coming out to be paraded about by the married man as his 'trophy'.
Many Er Nai lie to their parents and past friends about where the sudden influx of wealth has arrived from. Normally boasting a well paid non existent job.
The social status of an Er Nai is very low and can bring shame on their family and former friends.
How does it come about in the first place? - Because love is not the moral core of marriage here in China, as it is in the West, it is not socially frowned upon for a Chinese man to have his 'cake and eat it'.
The argument here is this - An Er Nai does not interfere with the marriage in any way because the man does not necessarily expect sexual satisfaction from his wife in the first place.
An Er Nai is often young with no social status other than 'beautiful trophy'.
She does not threaten the parenting skills or the social status of the wife and has no real desire to replace her.

The Green Cap is worn by the man, contrary to popular belief.
It is worn by him when he suspects or has proof that his wife is 'playing away'.
It is my understanding that it was originally used to show others that his wife had either gone or been thrown out by him because of her infidelity.
Concubines of ancient China
http://www.beijingmadeeasy.com/beijing-history/concubines-of-ancient-china
http://en.wikipedia.org/wiki/Concubine

China’s top court appears poised to side with wronged wives against philandering husbands and greedy mistresses in 2011.
Court Considers Revising China’s Marriage Law 
This contentious consumer group must be viewed in light of a deep-rooted set of Chinese cultural values, including the distinction between marriage and sex and the practical rather than romantic nature of the relationship 'transaction'.
Second wives and China's booming luxury market

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