One key building block of good marketing is promoting customer feedback. It's an old rule of communication that you aren't really communicating until the conversation is a two way street.
The benefits to hearing from customers are more satisfied buyers and frequent good ideas. Both complainers and complimenters can be a great source of improvements.
Often a happy customer will describe one of my services in an appealing way that I'd never thought of. Echo the things customers say in your marketing messages. Those customer written lines work best.
Encourage customer feedback by giving buyers a number of ways to reach you: toll free phone number, regular mail, email, and fax.
Rather than simply listing your phone number, include a line that says something like, "call our free number with your comments, concerns, and ideas. We love hearing from you."
It makes you look warmer, friendlier, more real, and more accessible. Those are the things that make people buy.