I have been mystery shopping since 2006 . Every shop is different even when shopping the same client. The locations can be in the intercity or a mall You must dress as other shoppers do and appear to be of the same demographic economically or you may not be buzzed int to higher end stores. .
In restaurants I believe many times they know you are the shopper because you are asked to perform the same requirements. They do not reveal you as they use you to report excellent service.
You notice them cleaning the floor and clearing the tables and you get your service faster than people who were seated after you. Sometime I write notes or appear to be on a shop just to get preferred service at restaurants I do not shop for but know they are being shopped. .I do not meet their age requirements but appear to meet their requirements.
You must view the customers entering the store, if your clothes and the language you speak and vehicle you drive does not match they may not even open the door if you are evaluating a high end clothing or jewelry shop; Halloween is my favorite holiday You dress up and stay in character even when it is not Halloween.