I have done eight of these fiery shops in mall locations and elsewhere. The timing (mm hh ss) at each of five spots, remembering every name of every person you encounter (did each use your name, say please, say thank you, ask if you want anything else), and the narratives can make your head explode. At least get the $5 app bonus (the app works occasionally, so there's that fun part of the narrative.) The food is pretty good and unless you really load up on ingredients, the calorie-count can be in the 650-or so per pizza (we split one.) The $18 reimbursement covers the pizza, salad and beverage. It isn't a "keep the change" shop meaning if you don't spend the $18, you won't get the remaining money as a fee.
And then there are the pictures: top, bottom, salad side and top .... Nothing says mystery shopper like asking a pizza to smile for its closeup.
As someone else said, online is the best option as you just have to get the name of the cashier and delivery person. The staff writes their names on their hats in illegible white ink on a tiny black background. No name means having to provide a long description.
As this chain grows, it will need a lot of shoppers. It is almost exclusively franchise.
Shopping SoCal and Maui.