A Best Buy customer relates the stirring 1999 tale of his refusal to let security guards at the store engage in their indiscriminate warrantless searches of his bags after he's paid for his purchases. He simply walks out, and whenever anyone tries to stop him, he just says, "Am I being detained for shoplifting?" and keeps walking. They even sent out people with pickup trucks to block him into his parking-spot!
Merchants basically have two rights covering people entering and exiting their stores. They can refuse to let you enter the premises and/or to sell you anything, and they can place you under citizens arrest for attempting to leave the premises with any property that you haven't paid for. But the second you hand over the appropriate amount of cash, they lose all rights to the items. They can't legally impair you from leaving the store with your property.
Apparently the employees of my local Best Buy aren't very familiar with annoying pedantic individuals who will choose principals over convenience when walking out with a shopping cart full of expensive home entertainment gear. I manage to get about 5 steps out the door before the door guard catches up to me and grabs my cart, with the "sir" in his "I need to see your receipt, sir" somehow not very complimentary. This is apparently a stalling tactic, as shortly a few more blue-shirted employees make a move to block me from making any more progress toward my car.
I ask, still calm, if I am being detained for shoplifting. This suggestion apparently shocks my captor into regaining some of his senses, and he lets go of my cart. I explain that unless he wishes to do so, he has no right to stop me.