Great question. Fakes are a huge concern when it comes to the rarer ones. For example, this guy: https://coins.ha.com/itm/byzantine/ancient-coins/ancients-me

Great question. Fakes are a huge concern when it comes to the rarer ones. For example, this guy: https://coins.ha.com/itm/byzantine/ancient-coins/ancients-mezezius-ad-668-669-av-solidus-20mm-448-gm-7h-ngc-choice-ms-5-5-5-5/a/3089-31080.s https://coins.ha.com/itm/byzantine/ancient-coins/ancients-me... Sold for $216,000 because it's both the nicest known and there are only 7 known from Emperor Mezezius. So the incentive to fake is high, but because there are only 7 to compare it to, experts would be able to spot the attributes of a fake pretty easily (even the best fakes always have some tell-tale giveaways). If you want to read a super cool story about a modern counterfeiter, Google around for the story of "Omega Man", a contemporary counterfeiter who created fakes of some early 1900s gold coins that were SO good that people actually seek out and collect the counterfeits today (he, like many con masters, couldn't resist an ego spike and left a calling card on his fakes...)