Payment due on receipt of invoice is better. Nobody except an enterprise really needs ten days to cut a check. With established clients, just match your invoice to their AP cycle, e.g. if they write checks on the 15th and 30th, invoice on the 14th and 29th...ok so it's a day instead of immediately. Retainer payable against final invoice is even better, then you're never upside down. And why should you be if being upside down is unacceptable to the client?