Free Goods Sales Order for Charities with Credit Limit

Dear All

I have a scenario where POS (Point of Sales) has been implemented,the process of POS is ok,but the requirement of the client is they are giving some goods to charity,when ever a person comes with a special card (Issued by the company) the outlet will create a sales order for the same without any charges with a credit limit of 1000 SAR (saudi arabian riyal).

Requirement

1) Creation of sales order with delivering goods but without any charges.(should have effect in Stock)

2)These charities is been treated as Customer with a credit limit of SAR 1000 (whenever the credit limit exceeds system should block the order)

how this scenario can be mapped in SD,

Thanks in advance

Malik