It has been a while, but I used to do mystery shopping. It was fun for a while, going to a store and rating how good their customer service was.
There is a company called Service Intelligence that is dedicated to helping companies to improve their customer service. According to their website, one of the ways they do that is by hiring mystery shoppers. Other ways include customer service surveys and offering training to the employees of their clients. I also noted that there is a link on their website to click if you want to become a mystery shopper. Maybe I’ll sign up with them!