There are usually three auctions available per day.
Special Auctions
There are also special auctions. These auctions are from a fourth vendor that will only appear if you have specific Pokémon within your boxes or party. These often provide special items for changing a Pokémon's form
Auctions
List of Special Auction Items
Rotom Catalog Auction if you have a Rotom in your boxes
Adamant Crystal Auction if you have a Dialga in your boxes
Lustrous Globe Auction if you have a Palkia in your boxes
Griseous Core Auction if you have a Giratina in your boxes
Flame Plate Auction if you have a Arceus in your boxes
Splash Plate Auction if you have a Arceus in your boxes
Zap Plate Auction if you have a Arceus in your boxes
Meadow Plate Auction if you have a Arceus in your boxes
Icicle Plate Auction if you have a Arceus in your boxes
Fist Plate Auction if you have a Arceus in your boxes
Toxic Plate Auction if you have a Arceus in your boxes
Earth Plate Auction if you have a Arceus in your boxes
Sky Plate Auction if you have a Arceus in your boxes
Mind Plate Auction if you have a Arceus in your boxes
Insect Plate Auction if you have a Arceus in your boxes
Stone Plate Auction if you have a Arceus in your boxes
Spooky Plate Auction if you have a Arceus in your boxes
Draco Plate Auction if you have a Arceus in your boxes
Dread Plate Auction if you have a Arceus in your boxes
Iron Plate Auction if you have a Arceus in your boxes
Pixie Plate Auction if you have a Arceus in your boxes
Prison Bottle Auction if you have a Hoopa in your boxes
Scroll of Darkness Auction if you have a Kubfu in your boxes
Scroll of Waters Auction if you have a Kubfu in your boxes
Reins of Unity Auction if you have a Calyrex in your boxes
Reveal Glass Auction if you have a Tornadus, Thundurus, Landorus or Enamorus in your boxes
List of Standard Auction items
Potion
Fresh Water
Soda Pop
Super Potion
Lemonade
Moomoo Milk
Hyper Potion
Poke Ball
Great Ball
Ultra Ball
Premier Ball
Heal Ball
Net Ball
Nest Ball
Repeat Ball
Dive Ball
Luxury Ball
Quick Ball
Dusk Ball
Timer Ball
Fried Fillet
Herbed Sausage
Horseradish
Curry Powder
Klawf Stick
Health Feather
Muscle Feather
Resist Feather
Genius Feather
Clever Feather
Swift Feather
Pomeg Berry
Kelpsy Berry
Hondew Berry
Grepa Berry
Qualot Berry
Tamato Berry
HP Up
Protein
Iron
Carbos
Calcium
Zinc
PP Up
PP Max
Sun Stone
Moon Stone
Shiny Stone
Dusk Stone
Dawn Stone
King's Rock
Metal Coat
Razor Claw
Cracked Pot
Chipped Pot
Bottle Cap
Gold Bottle Cap
Fast Ball
Level Ball
Lure Ball
Heavy Ball
Love Ball
Friend Ball
Moon Ball
Dream Ball
Source
The formatting for the auctions are a little weird but it makes them easier to export
