In order to sell you house/castle, you must empty it first. Sometimes we use the "pick up all items" button, but for some reason, it doesn't always pick up all of the flooring / wallpaper.
Go into your house/castle, and click on the button "place object" like you are going to put something in your house.
Then click on the tab to the left for "flooring and wallpaper only". This will give you a new button on the right to click on for "pick up flooring/wallpaper".
After your house/castle is empty, you should be able to go to a house dealer (or to the Bazaar?) and sell it.
Hope this helps.
Another Note: We have learned that houses/castles bought with the bundle packages are "No Trade, No Auction, No Sell, and No Trash". Once you buy them, you have them forever.