The can switcheroo
Me: Excuse me, do you know where the cans are.
Shop worker: in aisle three sir… uhh, do you seriously not know where the cans are? That’s really embarrassing.
Me: Actually, I do know where the cans are. I was just testing you to see if you knew, to keep you on your toes. And hey – good job.

The ol’ pasta sauce gambit
Shop worker: Excuse me sir. I rushed over after hearing the sound of glass breaking, and I note that you are now standing next to a smashed bottle of pasta sauce. Could you please explain what happened.
Me: Sure – a big guy smashed the pasta sauce and ran away. He was really fast, so you probably won’t catch him.
Shop worker: Ah, word up sir. It’s a pity I didn’t get here in time to catch the culprit.