Parallel traders in Hong Kong

Whilst we hear daily reports of the migrant/'refugee' crisis that is affecting the West, there is a similar but not quite the same problem here in Hong Kong.  In Hong Kong there is no goods tax similar to VAT, compared to the mainland, which is quite substantial.  Also questions arise in the mainland as to the quality of the goods for sale and to whether the products are genuine or fake.  So there is no surprise that lots of mainlanders make day trips to HK to buy daily goods such as groceries, detergents, cosmetics, electronics, nappies etc.  This has led to parallel trading where mainlanders come to HK to buy retails goods, take them back and sell them on for profit.  The result of this is that businesses in Sheung Shui, Fanling, Yuen Long and Tai Po - the north districts - or districts closest to the mainland border, get alot of business.  The negative side of this is that prices are pushed up for locals and indeed, locals experience shortages.  We know that prices are dependent on supply and demand.  This has led to anti-mainland sentiment and indeed anti-parallel trader protests.  I saw some of this myself the other day when we went on a visit to some friends in Shenzhen.  Once our train stopped at Tai Po, lots of mainlanders came on with their shopping, some were clearly parallel traders. 
Although this pales in significance to what the Europeans are going through, it does show how freedom of travel can have positive and negative effects on any community.