If you accidentally sell / delete / liquidate an item you are able to recover that item for a short period of time.
When you sell an item a "Recover Item" button will appear on the inventory screen. Simply tap that button:
On the next screen simply select the item you want to recover and hit the "Recover" button. You will find it in your inventory!
Be aware if you exit the game you will be unable to recover the item and it may be gone forever!