Who certifies that gold bullion is authentic depends upon what kind of gold bullion it is. Gold bullion coins, such as the American Eagle and the American Buffalo are backed by the United States Mint, a branch of the United States government. Gold bullion bars are guaranteed by the manufacturer. In this case, it is important to deal with long-standing and reputable companies such as Johnson Matthey, Pamp Suisse, and Credit Suisse. Reputable gold bar manufacturers such as Johnson Matthey refine gold to a fineness of 99.99% and assay to ensure the purity of their gold bars. Gold bars from Johnson Matthey, Pamp Suisse, and Credit Suisse generally come with a guarantee backing the weight and purity stamped on the face of the bar.
Bars of gold bullion from these great old names in gold are recognized for their quality. Subsequent certification or guarantees depend upon that assurance that someone did not go to the trouble of producing counterfeiting gold bars with the exact appearance of a Pamp Suisse bar, for example, and try to sell it. Such an item would be easy to spot because it would likely not look exactly the same and would not stand up to a simple assay technique, a drop of nitric acid. Nitric acid dissolves base metals and does not dissolve gold.
Another piece of good news for investors who purchase gold bullion in the United States is that the Commodities Exchange (COMEX) of the New York Mercantile Exchange largely regulates the American gold industry. This means that the NYMEX plays a huge role in ensuring that gold in the US market is legitimate and properly created.
The final line of defense in buying gold bars is to deal with established gold dealers and to buy the recognized names in gold bullion bars such as Johnson Matthey, Engelhard, Pamp Suisse, and Credit Suisse. A reputable dealer will also typically certify or guarantee that the gold bars he or she sells are authentic. Having a third party rare coin certification service certify gold bars does not add much surety and adds cost.