Covet inflicts damage and steals the target's held item if it is holding any. If the target is not holding an item or the user is already holding an item, Covet only inflicts damage and will not be able to steal an item. Held mail cannot be stolen.
The player's Pokémon's held item would not be stolen if Covet is used by a wild Pokémon. If the target's consumable held item is triggered by Covet, such as a Chilan Berry or Focus Sash, it will not be stolen.
All held items stolen from the player's Pokémon will be returned at the end of the battle. Covet will not steal a trainer's Pokémon's items permanently; however, a wild Pokémon's item is still permanently stolen by the player.