The Cloudy Moon Belt is a very outdated price, its range cannot be used as this price.

Also, one offer isn't enough to change it. (I suggest you take the belt if you're impatient like me!)

Like Soupman said, the belt's price was last updated 8 months ago. Also, the guy who offered you the belt is selling it for 7 buds, the hat is duped as hell: http://www.tf2outpost.com/trade/12512822

And the other owners want 9 - 10 buds (I didn't check if they were duped or not, but no one is selling for 11 buds). First of all, the belt's price should be updated and wait for the sale instead of an offer to change a price. Finally, when the offer is in unusuals, you must take unusual overpay into account: the price of the unusual in the middle and multiply it by 0.9.

Not seeing any evidence of your high end of 11.