Scarce is more common than rare. A rare coin has to be taken seriously, scarce merely implies they are hard to find now. So a scarce coin, may exist in a low number of thousands but is well sough after, or in the hundreds but less sought after. A rare coin, should only exist in the hundreds at most, and possibly only in the dozens. Rare coins ought to always command prices in the hundreds unless there isn't much interest in the area.