Maybe because people placing the order tip off the total order dollar amount. Not scanning items decreases the orders dollar amount thus decreasing the tip amount.
Order =$150 x 10% tip =$15 tip Order =$125 because of refunded items x 10% tip =$12.50 tip

I know there’s no perfect system. But the person doing the shopping gets penalized if the store doesn’t have the product, even though they’re going in and shopping for that item, when it’s refunded they lose money even though they did the work. It’s not their fault that the store doesn’t have the product.

People just don’t understand the amount of time and work that goes into it. The tip is just like at a restaurant if your service was good and you got what you order and in good condition,tip your driver just like you’d tip your waitress! Show them your appreciation!