How to sell items in PokeOne

Selling items in PokeOne is a bit different than most Pokemon games.  You can not sell items at all to shops.
There are purple tents located in Lavendar Town in the Kanto region and in Goldenrod City in the Johto region. These two places plus the Pokemon Fan Club in Vermillion City are the only places to sell items.
Here is a current list of sellable items to these NPCs:
– Nugget  (1,000 Poke Dollars)
– Pearl  (800 Poke Dollars)
– Big Pearl  (4,000 Poke Dollars)
– Stardust  (1,500 Poke Dollars)
– Star Piece (6,000 Poke Dollars)
– Star Shard
– Rare Bone (5,000 Poke Dollars)
You can, however, sell items to other players in the game.