I nominate the person who was price matching, whose order I had to re-ring, after she took advantage of another cashier.
I don't mind people who price match, I match myself, I save a lot of money that way. Throwing the phrase "I'm the customer, I'm always right" at me, will definitely not help your cause, neither will "I know the policy, it's in my car, so you want me to go get it?"
Having a fussy child won't work either. The child is your issue, if he's hungry, wet and tired, I will not give you what you want so I can get rid of you quicker.
You are correct, you don't need the ad, but it will take longer if I have to find the ones we have available to us, to verify your price. If you have a few things, I may not verify them, unless they seem way over board, but if you have a cart load, I will verify them. I can't afford to lose my job.
Your temper tantrum and crying will not help, either.