Rare 20 cent coins: Special misminting brings 825x profit. Some 1 euro coins can also fetch thousands of euros - as can certain 50 cent coins.
Anyone who discovers an incorrect embossing can try their luck as a private seller on the Internet - and use the prices of other offers as a guide. Large sums can sometimes be earned for particularly rare coins. But be careful: If you sell a coin or want to buy a rare coin, you should be sufficiently informed about private purchases.