That might be different for different products, and depend both on the local shops (might have different prices), on the fees of the agent shops (might have different fees) and on the exchange rate if you have to pay in some foreign currency.
So better check before you buy anything overseas.
Products in western countries are more expensive than in China, more and more word wide people manage to buy from Taobao, some buy with taobao agent service, with the shopping agent you have to pay service fee to them.
buy from local place or taobao price+shipping fee + service fee
which is more cost-effective?