Not to Exceed Estimate
Not to exceed contract.
The best option of all binding and non-binding estimates is the Not to exceed estimate.
This means that if the actual weight of your shipment is more than the written estimate, you still pay the amount quoted; however, if the actual weight is less than the written estimate, you pay the lesser amount.
If you ask for a not-to-exceed estimate, you'll never pay a higher price than what's on the estimate. In fact, you're price can only go lower. Whenever you get an estimate, always ask for a not-to-exceed.