(HELP)how to spot a fake balenciaga bag??

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the reason i've started this topic is because i've bought a real (i thought it's real) balenciaga bag complete with the receipt and everything, but then my friend bought a balenciaga bag from Hongkong with the price half from my bag and i even don't know how to recognize the fake with the real one?!? everything inside my friend's bag are similar with mine. the model, the tassle, the pewters, the serial number.. except my friend's bag doesn't have the receipt and the original box.if there anyone who know how to recognize the fake with the real one pls help me!! thanks for your all comments :))