In order to believe their story you have to believe that the delivery guy, for some reason, acted like a jerk and walked out with $7 dollars in change that they expected back then drove back with the change and acted humbly (if a little disgruntled). But apparently they didn't demand the change when he was there the first time and he thought it was a tip when he left with it.
So what would he have been acting like a jerk about if he thought they gave him a $7 dollar tip and they didn't ask for change at that time?
On top of that the manager gives out the first name of the girl he fired. That's class.
if you think the first tape would vindicate them, why would you fire them?
Lucy might just come back and torch the place