Honesty

 Sefer Chasidim (51) One is forbidden to engage in fraudulent and deceptive words, nor should he speak with one thing on his tongue and another in the heart. Rather let his insides be one with his word and that in his heart be that in his mouth. It is forbidden to deceive people including the gentile. And those who insult gentiles during an exchange of greetings while the gentile thinks that he means well, are sinners, for there is no greater deception than this