I think third party stories are an under utilized tool. It allows you to brag about your self or share some concerns you might need to share. For example: When some ask you "Why should I buy from you?" Of course you go negative and use the usual softening statements and then you can share stories why some of your clients have bought from you. You can use a statement like: Hmm, that's a great question, I hear that a lot. I don't know that you should buy from me. I won't know that until we have a conversation. I can tell you what my clients have told me. Some of my clients say after working with me they no longer accept "I need to think it over" and they have gotten out of the proposal writing business or you can give a specific example of a success story and then say, "I don't know if that is something you were looking for."
Try to think of these stories ahead of time, even right them down and practice them so you are ready. You never know when you will have an opportunity to share a story.