Why not check online after receiving the goods, and then pay after confirmation, otherwise you can return them. Generally speaking, there seems to be no one who can find precious metals online. Only jadeite can be found on the websites of relevant institutions. As far as I know, generally speaking, commemorative gold bars issued by China Gold Coin Corporation have appraisal certificates, and I have never heard of any codes. If it is a gold coin, there is also a certificate signed by the Governor of the People's Bank of China.

I suggest you take the gold bars to the jewelry store and trade in the old ones to see if they are pure gold. If not, you can complain directly to the merchant. You still need to find a reputable store to buy things online, and don't be greedy for cheap.