Forget about writing you for information - capitalize on their impulse. That's easy - you get responses. Does that mean sales - no. It means responses. The sales part is a whole different animal.
Advertising online is the same.
You cannot expect your ads to generate leads if they are only done once or twice, or by using a shotgun approach. Consistency here is the key - keep your offer in front of your prospects on a regular basis. Don't be afraid to experiment with your ad copy. Keep a notebook which has copies of your ads with one per page. When you get a response, make a note there and include their E-mail address.