There is NO LAW that states a tenant must pay his LL's mortgage fees whether they were incurred from late payments, bounced checks or not...
In this case the LL is SOL as he can only charge what is in the lease... IF it states in the lease that the LL will charge a $50 NSF fee, than that is all he is entitled to, and anything that is in AZ LL/T laws...
In this case, the argument you mke that the tenant should have had enough money in their account to cover the check can be made for the LL... The LL should have made sure they hadd enough money in their accounts to cover the check they wrote, REGARDLESS of a tenant paying late or bouncing a check...