Even on Facebook Games there are people that sell in game items for real money. I never saw the use of it for games like this myself. I guess it depends upon the item, the player and the benefit the player feels they get from the item.
I use to play an RPG where, when you hit the level cap, you could unlock an ultimate mode character that had better skills, more power and way more stats. The drawback was if you died in game and didn't have a resurrection stone on you or a healer to resurrect you, your character would be wiped along with any equipment they had in their inventory. I paid real money to the game company for rez stones because I had invested a lot of time into building my character and equipping her. I stopped eventually because I found that I enjoyed the game less when I had to pay real money for something that would allow me to play in a game world.