Why would you say "okay" when your answer is really "no"???

Just say no. Your answers aren't clear. He's going to think you're interested when you're not. You shouldn't confuse him or give him false hope. Being honest and direct isn't rude. Pretending he has a chance is rude and you'd be lying. In your pursuit of being "nice" you're just setting yourself up for harassment and actually being not nice.

I suppose you could say those things. Korea is probably no different from any other country in this regard. Here's the Korean versions of those phrases, in a polite style. "Okay, but it's not a promise, okay?" => 그래요, 근데 약속할 수는 없어요. 아시겠죠? (the last part makes it harsher) You could make it softer (and vague), by saying (그래요,) 생각해 볼게요 (I'll think about it). "I'm not really sure yet" => 글쎼, 아직 잘 모르겠네요 / 아직 확답을 못 드리겠네요. * 글쎄(Let me think ...), 아직(yet) 잘 모르겠네요 (I am not sure). => Well, I'm not sure yet. * 아직(yet) 확답을(firm answer) 못(can't) 드리겠네요(give you) => Can't give you a firm answer yet.