From the Super Mario Wiki, the Mario encyclopedia
The Information Booth is a store in Beanbean Castle Town that specializes in selling information. The shopkeeper sells "information" to Mario and Luigi for 100 coins, and this information usually revolves around their current objective and either where it is located or how it can be accomplished. His information only relates to the main story and nothing else. Near the end of the game, when Mario and Luigi are ready to go to Bowser's Castle, the Information Booth has no more information to give.
In Mario & Luigi: Superstar Saga + Bowser's Minions, the shopkeeper of the Information Booth no longer sells information to the brothers, and instead looks at the player's records, awarding items based on their progress with Blocks, Beans, the number of battles won, the number of enemies defeated, the number of Excellent attacks done and the number of battles fled from. After fulfilling all of the requests, the shopkeeper is satisfied and leaves the shop.