People started counterfeiting money not long after coins were invented in anceint Turkey about 600 BC. I have a fake Athens silver tetradrachm from about 200 BC, it's silver plated but inner core is cheaper metal.
We do need to be careful, there's a lot of fake modern coins. For example, in China there are severe penalties for faking their own coins/currency but none for them to make fake USA coins. In China many fake Morgans,
Peace dollars, fake
ASE have been made. People not aware buy them online, they think they are getting a good deal buying a silver eagle way below melt price. There's also fake gold eagles etc. In Europe fake USA coins have been made, pre-1933 gold, etc.
It's always wise to buy from well known online dealers and good coin shops. I don't know if the recent surge in silver/gold prices will cause more counterfeits, it sure could, fake coins, fake bars, fake jewelry. Sadly with newbies starting to buy silver/gold they may get cheated.
There's Youtube videos of collectors showing fake coins, interesting to watch. For myself I use a weight scale, caliper, magnet, ping tester and if need be my local coin dealer has an XRF and Sigma, he tests coins/bars for free. He has people come to sell stuff, some test as fakes unfortunately.