Why You Need China Sourcing Agent?
Most of the sellers on Taobao/Tmall/JD are individuals who are most likely not well versed in English. As a result, miscommunication is bound to happen, and money will be wasted.
Most of the sellers have no experience in international shipping. Even if they do international shipping, you may be buying from many different sellers, and you will not be able to save shipping costs from combined shipping.
Credit card has yet to penetrate China to the extent that it can be a common online payment method, so most online stores in China do not accept VISA, Mastercard, or American Express. Although Paypal does have a presence in China, it charges outrageous withdrawal fees for international payments, so sellers are unwilling to accept payment by Paypal.