Watch for Chinese coin fakers. They have a huge presence on Ebay with coins that look good, but some have huge errors, wrong years, wrong mint marks. They also do it with other old coins. They are into the $10-$50 coins. The Tungsten coins that are all over China now are so valuable that few buy on Ebay. Sonic chirp meters detect them. On youtube = fake gold china will give hits. One good method is a scintillation detector. Few old gold coins or Roman/Celtic coins have any nuclear isotopes from WW2 or the atmospheric test era. Geiger counters are usually not good enough. The modern fakes are easily spotted with the correct scintillation detector, which has a fair sized scintillation stone. The low cost ali-express radiation detectors are a lot less sensitive