How do you know your supplier bullion is genuine?

Quoting an officer from the Royal Canadian Mint, the best way to ensure authenticity is to buy from a reputable dealer. We are a primary distributor for The Perth Mint which in turn is owned by the Australian Government. We are also a direct distributor for the Central Bank of Mexico (Banco de Mexico). In addition, we purchase directly from LBMA Good Delivery refiners such as Metalor (Switzerland) and Nadir Metal (Turkey). For all other bullion we go through the largest American physical bullion distributors, one of which handles over half of the Royal Canadian Mint sales and more than 40% of US Mint sales. If there are any doubts we willl conduct a DUX Test.