I think the most important thing in business is getting the orders in the door, but the number one problem is getting paid for your work.  If you have a diverse base of customers who do pay on time, you can afford to have a late payer in the mix.  The late payer should be providing you with a steady stream of orders and be consistent in payment.  I would have no problem accepting late payments on a high volume customer, I would just budget it in.  The thing you need to watch for is if business in general declines and you are holding too many receivables.