When an order is created, the purchaser becomes liable for payment of the full amount of the order, under normal terms of commerce and business law.
Some purchasers prefer to have their liabilities better defined. They request a form of payment which is really a 'pay as you go' approach, where they're only liable to pay for what they've received.
Since the normal terms of trade are full liability on the purchaser, they will require a letter of acceptance showing the terms of their payments and liabilities.
Note: Upon issue of a letter of acceptance of these terms, you are committed to the arrangement. The letter is prima facie evidence of your terms of sale.
These terms apply to sales to a private individual or another business.
You may include exceptions for default, partial, or non payment, in your letter of acceptance. The purchaser must agree to these terms in writing.
It is not good practice to enter into any unclear arrangement for payment on these terms.
The example below relates to a series of shipment of goods over a period of time, where the entire order can't be delivered at once. Under these circumstances progressive payment is a reasonable (and understandable) request.
Re: Proposed terms of payment
I refer to your letter / email of (insert date) requesting terms of progressive payment on delivery for each shipment of your order(s), rather than full payment of the amount due.
These terms are acceptable, with the following exceptions:
If a due payment is not received within 30 days of delivery, the amount payable on the whole order becomes payable in full. Partial payment for shipments will not be accepted.
If you agree to these exceptions, please respond in writing indicating your acceptance of these terms.
If you do not agree to these exceptions, please reply stating your preferences.