networkn:

 

How many non-lawyers would reasonably be expected to know that snatching a bit of paper from someone would be assault under the crimes act (I'd be interested to see if a conviction has ever been obtained under such circumstances) vs the wrestling of said receipt back from someone physically? 

 

It's appaling customer service conduct no doubt, but escalation to an onsite manager would have been a far far more appropriate and effective way to resolve the situation and would likely have resulted in a much more serious consequence for the staff member in question.

 

Ignorance of the law is no excuse. You don't apply an unconsented force upon another's body (directly or indirectly) without justification (again, I am taking the OP's description of a wrestle literally) because that's wrong. I learned that basic rule of being a morally decent person -- laws aside -- at school. This also rather closely maps to what the law defines as an assault. You really need to do more thinking.