From the Super Mario Wiki
“I'm all out... If you want to hear another story sometime, you know where to find me. ”
Carson is the owner The Overthere, the coffee bar (described in-game as a "beveragarium") in Flopside in the game Super Paper Mario. For ten coins, Carson will tell one of approximately fifteen stories he has collected over the years. They range in scope from the Pixl uprising to Count Bleck's minions. If the player does not have enough coins, has listened to all of Carson's stories or does not accept the 10 coin charge, he will tell one the player has already heard before for free.
His Flipside counterpart is named Garson, and while Carson sells coffee, Garson only sells milk at his bar, The Underwhere. Both establishments are name after the realms of the dead as seen in Super Paper Mario, The Overthere and the The Underwhere. Carson and Garson take the roles of Russ T. and Wonky from the past two Paper Mario games. The original Paper Mario's Russ. T offered much more information throughout the game and would tell it for free, while in the sequel, Wonky had a wider range of topics and would tell them for five coins.