A number of mystery shopping companies have restaurant shops. The restaurant clients of mystery shopping companies are very regional so your particular location would determine which companies shop the restaurants you might be interested in. The best thing to do is to sign up with a lot of mystery shopping companies. You should definitely be registered with at least 50 to see a good variety of shop. Most of us here are signed up with over 100. See the blue link at the bottom of the page, Official List of Mystery Shopping Companies, for a list of almost 200 companies to sign up with.