I did this shop and it was enjoyable. Like Cettie, I wrote a completely ridiculous essay (mine was a barely-intelligible rant about pimps and @#$%&). I finished the test in about an hour, as the instructions said, and I was not the first test-taker to finish.
I was not instructed to try to bribe the exam people, but I did have to whine about not getting a better score to see what they said.
Do NOT try to take an audio recorder! You are only allowed to take your ID and locker key into the test room, and they visually inspect you and require you to turn out your pockets before entering. Oh, and I was instructed to leave something in my pocket and see if they found it and how they handled it.
I had fun with all the covert stuff (and writing my crazy rant) and it was decent pay for the ease of the assignment.