I did this shop in December. On the piece of "hidden" paper, I had the address of the test taking facility. They make you empty out your pockets and pat yourself down before you go into the room. 2 people, in fact, in 2 spots did the pat down procedure. They spotted the paper, so I just threw it in the trash. The most annoying issue was the raising your hand twice to call a proctor. The first time, I told the proctor my screen was dirty and distracting me. The second time I went to the bathroom.
The requirements say you have to remain in the room for I think, 50 minutes. I was the next to last person to leave the room. I suppose we are monitoring the other test takers also, to be sure the proctor's don't allow anything. Even still, everyone else finished the test a lot sooner than I did.
I did fail, and I really did feel bad because I hate failing things. So, when it came time for my printout, I just said, "Is there anything I can do to make this better?" The lady at the desk just looked at me and didn't say anything. I didn't do an obvious bribe. But, the requirements just say ask what you can do to pass. I filled out my report stating what I just told you, and it was accepted.
It has to be somewhat obvious/predictable we are mystery shoppers at some point in our visit, but I suppose the proctors don't really know at first. It still keeps the proctors 'on their toes' to do their jobs right. It is possible a normal person could need to use the bathroom or have a scrap paper in their pocket too. Good luck and have fun on the shop!!