Due upon receipt

SOLVED

Hi,

Our invoices come up as :

Term: Net 30. Due (date)

that is fine with the majority of our clients but a few of them do not have good credit and we want them to pay upfront BEFORE we send them the results (we are an environmental lab).

Is there an option to custom that field for each customer?  I know i can change it to say due in 0 days but that is not really telling the client that its due upon receipt... any idea?