I’ve been Playing Mystery Dungeon a Long time ago.
The Roles are Swapped.
NPC Shopkeepers are Pokémon except Kecleon who is a Player Rescuer.
The [Your Pokémon here] shop in the Dungeon while Kecleon is a Thief not a Rescuer. The Shopkeeper Pokémon will become Hostile. The Other Pokémon at the Highest Stats will Spawn.
For Example: Kecleon steals Invisify Orb at the Gardevoir Shop they will turn Angry for stealing.