A: Have you decided to invest in their project?

B: I don’t know. This plan still sounds pretty risky to me — I’m not sold on it yet. How about you?

A: After seeing their presentation, I’m sold on this investment. So I’ll go for it.

Note: “To sell someone on something” means “to convince or persuade one to do something or to accept some plane or idea.” It’s often used in passive constructions, meaning “totally confident in or convinced of someone’s or something’s viability, veracity, appropriateness, skill, etc.”