I just left this comment elsewhere: Humans project. What people think of others can tell you too much about them.
The best piece of dating advice I ever saw—and I wish I could remember where I saw it—was to pay attention to how your date treats the people who serve you. People who treat some people badly will treat anyone badly.*
In Dogland, the father tells a story my dad used to tell: A man is thinking about moving to a town, so he asks a local what the people are like. The local asks the man what they're like where he comes from. The man says they're a lousy bunch of no-account sons of bitches. The local says, "You'll find folks here are just like that." That man decides to look elsewhere. Another man comes to town and asks the same local what the people are like. The local asks what the people were like where this fellow came from. He says they were the kindest, most wonderful folks you could imagine. The local says, "You'll find folks here are just like that."
*When I read bell hooks' "Killing Rage", all I could think was how impatient she was with the people she saw as the serving class.