To the best of my knowledge it is simply someone offering advice for doing mystery shopping. I don't know if there is a cost as I have never investigated it. Certainly most of what you need to know you will find on forums and by asking questions here because folks are good about giving you a considered answer.
I get emails for Mystery Shop Maven all the time. It is just free advice. I've noticed some of the people posting get confused and think She sends jobs or something.
Yes, it is remarkable how much confusion there seems to be. Folks don't seem to get it that signing up with this forum and announcing you are ready for folks to send you work is not how it happens. Or that posting your location on the job board is not how it works. Oh well.