Customer relations experience

How do you approach customers when responding to enquires? Professionally I’d hope, and respectfully too. But do you talk down to them, dumb it down almost to child-like level that it feels belittling? That was the experiencing i just had with one company where I honestly felt like I was being told I was dumb. Is this good customer relations? Will it win you repeat clients? Not this one it won’t, it will be a one time only transaction from me after that experience.