I'm very selective on the wants ads I respond to. If I have something, and I feel that they are genuine (sometimes quite easy to get that vibe), then I'll get in touch. It's not at all often I do respond, but the one ad I responded to recently did result in a very happy, smooth transaction.
Generally, I find a sizeable amount of people who post wants ads either lack the good manners to respond, or are just daydreamers, freeloaders or tyre-kickers, and that's why I don't go out of my way to help the majority of wants, if I have what they want.