The manual entry for ratlings states "These humanoid lean and wiry rats thrive in larger settlements and enjoy interacting with other races. (...) No matter what they are accepted as skilled traders, quick warriors and crafty thieves". Their status as natural traders and barterers is also reflected in their skillset (which includes Appraising, Detect item status and Haggling). However, their Charisma stat seems to be, on average, lower than average (i.e. lower than a human's average). Ratlings' natural Charisma values should be adjusted up to match the rest of what we know about ratlings, both PC and NPC.