USPS Priority mail is not a guaranteed and does not come with a money back guarantee.
What is UPS Surepost? UPS Surepost is a new shipping option we've recently added. Surepost is where UPS will pick up and handle most of the trasnportation except for what UPS calls the "last mile". UPS will deliver your package to your local US Post office and the USPS will handle the final leg of the delivery. In some cases if UPS determines they have another package being delivered to your location on the same day, UPS may handle the final delivery.