In the games, badges affect a Pokémon's behavior. A symbol of competence on the Trainer's part, badges force traded Pokémon under a certain level to obey. Additionally, Trainers cannot have a Pokémon use an HM move outside battle without the appropriate badge. Also, beginning in the fourth generation, the number of badges a Trainer possesses affects which items Poké Marts sell. The more badges, the more items that become available for purchase, with more expensive items generally appearing after more badges are obtained.