I don’t have a problem showing my receipt. It’s not “paid” items they are worried about, it’s people walking out with “unpaid” items and personally, I believe they have a right to look at a receipt and make sure items, particularly large, expensive ones that are obvious in the cart, are all “paid”. Just having someone posted at the door is a deterrent - I wouldn’t want the job because some shoplifters have gotten violent when employees have tried to stop them.
Unlike most Americans, I still believe in the US Constitution as written.
Amendment 4: The right of the people to be secure in their persons, houses, papers, and effects, against unreasonable searches and seizures, shall not be violated,
Stop them? My brother-in-law was a long-time employee at Walgreens in San Francisco. Store policy is not to confront shoplifters. So employees can only stare at the black thieves as they walk out with merchandise. Yes, almost always black.
He's been yelled at by thieves as they leave, with "You hate black people, don't you!" - and he's been punched in the face just for looking at them without saying anything. Even a black co-worker was punched. B-i-l finally retired a couple years ago, fearing for his life.