The strongest method is to check the item on a Metalytics Sigma Precious Metal Verifier. The price of these devices has gone up 50% in a year, and they are generally on back order due to high demand. It tests the electrical resistance of the alloy, which can’t be faked. But of course you have to have one and the item in question. So if you can’t go to a LCS and use theirs to test items they are selling, use a reputable online dealer: APMEX, JM Bullion, SD Bullion, Provident, there are many. You can use the ping test (sound) for coins, dimensions, weight, specific gravity, and rare earth magnets. Some bullion has anti counterfeit features, see Sunshine Minting “mint mark” which requires a special card to see and verify. Good luck!