我们要通过一个人如何看待服务人员来判断人品

If you want to know whether a person is really nice, observe the way that person treats salesclerks, waiters, and other people in service professions who can't defend themselves. 

如果你想知道一个人是不是真的友善，那就观察一下那个人如何对待售货员、服务员和其他无法为自己辩护的服务行业人士。