Precious Metals
There are a number of websites useful for buyers and sellers of gold and silver. Here are a few we think are most important.
LBMA
https://www.lbma.org.uk/good-delivery/about-good-delivery
The LBMA (London Bullion Market Association) maintains the Good Delivery List, a set of standards for the production of gold and silver bars used in the wholesale market. This international trade association represents the wholesale over-the-counter market for gold and silver bullion and specifies the rules that gold and silver bars must meet to be accepted for delivery in settlements in the London bullion market. This list is a good starting point to help determine if a refiner or sovereign mint has a good reputation for producing precious metals at expected purities.