Have noticed that some stores have cut down the self-checkout & they have 2-4 persons WATCHING the self check out, plus a person checking your register tape against your basket.
THOSE “WATCHERS” could be actually checking instead & give up ALL the checkouts.
Keep in mind that you are under no legal obligation to allow the store to examine your receipt at the door. At that point, the stuff in your basket is your property and they don’t have the right to make you prove it.
As Dionne Warwick sang: Walk on by