This is called the “halo effect”. An initial favorable impression (such as perceiving that someone is physically attractive) biases us to attribute unrelated favorable qualities to them. Study after study has born this out.
In the criminal justice system, more attractive criminals are consistently treated with more leniency (unless it was judged that their attractiveness was used to facilitate the crime). source
People are more willing to anonymously help an attractive person. source
People are more susceptible to persuasion by an attractive person. (“Communicator physical attractiveness and persuasion” Journal of Personality and Social Psychology. 1979 Aug Vol 37(8) 1387–1397)
Attractive children are less likely to be considered rotten by adults when they misbehave, and teachers are more likely to attribute intelligence to attractive kids. source