Statistic about the success of my coaching program…

Hi Brooke, or any master coach 🙂

At the end of free mini coaching session I am very often asked if I have some statistics to share about the “success” of my program.
I am always answering them that I don’t have these kind of statistics because they mean nothing about their own success. And the only way they can be sure that this will work for them is if they are willing to invest enough time and energy to apply it in their life, and do exactly what I told them to do…
I have the impression that this is bringing them more doubt than it gives them confidence.
What would you suggest then ? Should I continue to coach them and show them how they are now creating these doubtful thoughts because I don’t want to give them statistics ?
Or do you think that I am the one creating this doubt in them by the way I am communicating my answer to them (I don’t have these kind of statistics … etc…).
Thanks for your answer.