When a local TV station wanted to find out how five stores measured up for customer service, they hired an experienced mystery shopper to investigate for them. This video tells the story.
In regular mystery shopper jobs you would evaluated more than just how long it took to get store employees to help you and help helpful they were when they did assist you. You could be asked to look at how certain products are arranged or stocked, how clean the store is inside and out, how clean the restrooms are, and how efficient the cashier was when you made your purchase.
Each mystery shopper job has a set of requirements that you need to study ahead of time so that you can remember to observe each thing and then report on each item on the evaluation that you will fill out. Being observant from the moment you arrive is very important. You probably will have to report your beginning and ending times as well.
The more shopper jobs you do, the more confident you will become and it will become easier to remember every required detail.