Anyone who buys gold online should have a tester, and there are reputable bullion companies like JM who don’t charge a lot of markup. If you’re on ebay trying to buy gold bullion there’s a chance it’s probably fake / silver wrapped with gold and stamped. There’s videos on the internet of folks cutting those bars in half and seeing what’s inside.

A way to increase your chances of buying real product is to buy coins that are in bad enough shape where there’s no numismatic value left. Whereas every country that mints coins has strict laws against counterfeiting them and you can go to prison for doing it, making “novelty” gold bars and rounds is perfectly legal and there’s almost no risk if you get caught scamming people with them (most often just a platform ban).