I'm a little uncertain about repeat customers, Erin: I thought I remembered you saying somewhere about people who'd say 'should I book a time for next week?' with your response being (roughly) 'did you just hear what I said and plan to put it into practise or not?'. My overall impression, therefore, was that your readings weren't something people had to/should repeat very often, only when the previous reading was no longer relevant.
I hope I've expressed that clearly enough. I guess I'm just a bit unclear on the point of 'repeat' customers, which sounds like regular or at least semi-often.