When a mystery shopper accepts an assignment, that is a commitment to follow through and do the shop. A shopper who doesn’t complete an assignment as agreed risks being deactivated from the mystery shopping company’s data base and receiving no future jobs from them.
Schedulers get frustrated when shoppers cancel at the last minute or just fail to do a shop. It happens more than you might think. In fact, it happens often enough that we have an industry term for it: It is called “flaking” on a shop.