I'm having a problem coming up with a business model other than advertising.
I did a little research, and it seems to me that people are paying for features/services that
deals with inconveniences.
the thing is, our basic(free) service does that and I'm 100% sure no one is willing to pay for that.
but lately I'm thinking about customization feature. so what i want to ask is, when do people pay for such complementary features(that doesn't affect functionality)?
What does your product/service do? Without knowing that it's really hard to answer this question. I suggest you add that information in your question if you want to get quality answers. Based on the little bit of information you provided, here's what I can offer/suggest:
I would suggest taking another survey (assuming you've already taken one) among likely users, and including different price points along with asking them what features they would want to see.
I hope this helps!