I gladly show my receipt at Walmart as I am leaving, even when I am not asked.
The greeters have a thankless and sometimes hostile job. Why can't I be someone who doesn't mind making their life easier, if only just for 5 seconds.
I show my receipt without hassling the door greeter, and I am always nice to them. I still think it is a bad policy and they could find a better solution to shoplifting or employee theft.