If the actual postage cost is significantly less I'll refund the difference.
Many previous customers have been pleasantly surprised to receive an order with cash back!

The Postage Promise.

If the system has not charged enough postage, you will never be charged any more. 

If the system charges too much postage I'll refund any significant differences myself and either the full amount will not be debited and you will be informed of the actual total debited or you will receive either a cheque or cash in your order.

The postage costs on this site are calculated by a formula depending on the weight and delivery destination of each object purchased. This formula is 100% accurate when single items are purchased, however in about 5% of multiple purchases, depending on what items you purchase and in what quantities the automatic postage cost can be either not enough or too much. With my postage promise you are guaranteed to never pay more than the actual cost of posting your order.

Chris Perkins, Predecimal.com