Quick Answer: Parcel carrier service guarantees are promises that UPS and FedEx make to deliver your package by a specific time. If they miss that deadline, you are entitled to a refund on the shipping charges. Most businesses never claim these refunds simply because they do not know they exist or do not have a process to catch them in time. What Are Parcel Carrier Service Guarantees? When you pay for a shipping service, you are not just paying for the package to arrive. You