I am old and thus I still remember these pretty days of Diablo I, back in 1996 -- where each and every pieces of Tristram was filled with a pile of 5 000 gold pieces (the biggest amount you could store in single map's cell) -- because Diablo I's economy had so poor design that most of the players were earning millions by the end of the game, without a real ability of spending this.
Game economy is an extremely important part of each game design and you are deeply wrong, if you think that it plays key role only in economy-based games. I have intentionally mentioned Diablo 1 to show you an example of a dark fantasy game. Some economy-related mistakes for match-three like game are also mentioned here.
In this article I would like to focus on some economy-related issues and mistakes that you must consider when designing money and resources layer in your game, no mater what kind of game you're currently developing.
Crafting is an important part of game economy, but I have written a separate article on this subject.