"There are a LOT of
No the same other thing could be causing the negative correlation, or two other things, or three...
If the queues are all too long I will dump my pile anywhere and walk out: in the hope that the manager will realize that this policy is costing sales and re-stacking time.
Aldi charges a fee for providing a cart, even though some are usually available for free outside in the car park. And, it charges a percentage fee for using your credit card. Traditions from Germany, I guess.