On this coin from ancient Greece, Hercules on the front is adorned with a lion's scalp and Zeus on the back is holding an eagle and a scepter. According to Stack's Bowers and Ponterio, where this image comes from, these were struck during the reign of Alexander III (the Great) 336-323 BC. Stack's coin is a silver (AR) tetradrachm weighing 17.08 gms. It sold in a 2011 auction for $750 US dollars.
The $750 hammer price for the Stack's coin gives you an idea of value for nice specimens of these amazing coins. Wear and damage would lower the price significantly, as explained below. But what REALLY lowers price is if the coin is a counterfeit.
The coin in our second picture was selling on eBay as a genuine tetradrachm. But it's a fake. See the Fake Reports (click here) on forumancientcoins.com. This is a modern cast counterfeit worth zero.
Side-by-side inspection of a genuine and counterfeit coin, as on this web page, sometimes reveals the truth about rare coins, but not always. Always deal with people you trust when buying rare coins.
Consider the three coins in our last picture. They are labelled (A), (B), and (C). The (A) coin is a superb example of this piece, with sharply struck, clear surfaces and exceptional eye appeal. It sold for $900 US dollars in a 2015 auction by Ira and Larry Goldberg. The (B) coin lacks the appeal of the (A) coin, and the price is substantially lower, about $150 to $250. Finally, coin (C) is a high-quality museum replica in silver with a value of about $25.