Both shops in operated by the characters Polendina and Pulcinella can be upgraded when Pinocchio delivers specific items back to them in Hotel Krat. Doing this expands the number of items each vendor will sell to Pinocchio along their journey. Ranging from new weapon parts to additional Legion Arms and other useful upgrades, increasing the stock of these stores should be a top priority as you explore Krat.
There are two other vendors in that cannot have their shops upgraded like the ones in Hotel Krat. One is the Wandering Merchant, who simply has more goods when you meet them after progressing through other parts of the story. The other is Alidoro the treasure hunter, who has only a few items for sale, but mainly exchanges Rare Ergo from bosses into special gear rather than have a selection of their own.
Related: Lies Of P: Should You Kill Alidoro?
You need three Supply boxes and three Venigni Collection items to upgrade Polendina and Pulcinella's shops respectfully in. While the former shop can be interacted with right from the front desk of Hotel Krat when you first enter the building, you have to beat a couple of chapters to unlock Pulcinella. The second NPC store will become part of the Hotel after you rescue Venigni from The King's Flame, Fuoco boss in .
Upgrade Item
Location
How to Find
Krat Supply Box
St. Frangelico Cathedral Chapel
Go to the wooden tower with multiple prison cells in this area. Battle your way to the top and defeat the puppet with a massive shield guarding the last few cells. A chest in one of the empty cells here holds the item.
Strudy Krat Supply Box
Grand Exhibition Hall
Right before you fight Champion Victor, travel around the corner next to the entrance next to the boss fight arena.
Read more on screenrant.com