I often do shops for a grocery chain and one of the questions they are supposed to ask is "Did you find everything you were looking for?"
You are required to make a purchase (reimburseable up to $2). Last time I went, I bought some female hygiene products and the young teenage cashier did not ask me the question. I was not trying to test that out but I genuinely needed that item.
I imagine that it would be an awkward question for a cashier to ask if you came to the register with a box of condoms or something similar... but I would never do anything to get the employee to mess up on purpose.
Anyone else think about something they would like to do but would never actually do during a shop?