Because they are not a well known company, that's why they can do what they want. If you work as a CS in a well know company, like CLP, MTR, PCCW, HSBC etc..... they will not allow staff to do this and they need to smile back to you even you treat them badly. So, don't work as a CS in a large company :DD
Also a large well known company will always say "Customer is always right !!!" You cannot expect the same kind of CS from small companies. But of course you need to spend a lot of money on CS since many customers are really unreasonable and you cannot expect a small company to invest such kind of money in CS.