We have retail customer, our order to delivery would generally take from 1 week to 3 months or more, depending on the products our customers select. We deliver the products in different batches. Our policy is to have a minimum 50% advance payment to confirm the order. We collect payment in advance, please have an option to restrict creating or approving an SO for which the certain defined amount(50% in my case) is not available as advance. Upon invoice or delivery the remaining amount against the product delivered value would be collected. Top level exception approval has to be taken when such SO, invoices and respective delivery has to be made without advance payment.