TinyCo has written a guide on how to sell your unwanted items!
“In the latest 1.2.1 update, we introduced a selling feature. Now you can get rid of your unwanted items and earn back coins! You can sell items directly from your inventory or while in decorating mode.
To sell from your inventory: tap on the ‘Menu’ icon (the icon in the bottom left corner filled with squares). From there, tap on the ‘Inventory’ icon and look for items that now have a small blue “$” button in the top right corner. Tap on this button to bring up a “Sell Item?” screen. From there, you can confirm if you wish to sell these items for the amount of coins listed. When selling from the inventory, you will sell ALL quantities of that item owned. For example, if you have 4 Baby Party Palm Trees, selling from your inventory will sell ALL four.
Here’s the confirmation screen from selling from your inventory. Please note this will sell ALL quantities of this item you wish to sell. In this case, you will sell all 4 of the Baby Party Palm Trees currently in your inventory.
If you have multiples of an item in your inventory and only wish to sell one, you will need to place the item from your inventory into your Quahog and sell from Deco Mode.
To sell from ‘Deco Mode’: tap on the ‘Decorate mode’ button (the icon with the four arrows) and select the item you wish to sell. If this item is sell-able, you’ll see a new “$” button appear alongside the rotate and inventory buttons. Tap the dollar sign to bring up the “Sell Item?” screen where you can confirm if you wish to sell.
Here’s the confirmation screen from selling from Deco Mode. Selling this way will allow you to sell one item at a time. Confirm the transaction by tapping on “OK”!”
Hope this has helped anyone that was having troubles!