Humans are notoriously prudish and petty, but they are extremely loyal to their friends. They value honesty and hard work, and hate lazy people.
Everyone agrees that Humans make excellent traders and negotiators.
Elves say: "They're rude and greedy. And for how much they hate sex, you'd be surprised how horny they are. Oh, but they make great friends! They love trading."
Rakshasa say: "They're trustworthy merchants and they make charismatic leaders. They love feeling in control... it makes them happy. They work incredibly long hours."
Orcs say: "The smart ones have silver tongues and can trick an orc out of his breakfast. But the dumb ones are dumber than any orc! Their warriors are no match for orcs, but their wizards are feared. Human merchant camps are neutral ground, so try not to burn those down too often."