That's a very good idea. My gym nominated this week as "Feedback Week" and everyone attending a class was given a form to fill in to rate the teacher on different attributes, as well as to make suggestions or comments.
Perhaps Ceroc (either centrally, or each franchise individually) could have reply-paid postcards printed on which you could rate a class and venue 1-5 on various categories and put it in a box at the venue or in the post if you preferred.
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