These are the most common reasons why you have noticed different shipping rates in Ship&co:
1). The shipment details that you have added inside Ship&co are different (i.e. the dimension and size of the parcel you have entered in Ship&co is different from what you see on your carrier's fee list, or you have added optional services in Ship&co that will require an additional fee, etc)
2). Your discounted rates are not yet updated in the carrier's system.
If you start using Ship&co within a few days of opening an account with a shipping carrier (FedEx, UPS, or DHL), the agreed/discounted rates might have not yet been reflected in the carrier's system and the general/published rates might be displayed as the estimated shipping cost. However, even in that case, your agreed rates will be applied to the actual billing from the carrier after shipment. Please contact the account manager of your shipping carrier (FedEx, UPS, or DHL) for more information.
The estimated shipping rates displayed in Ship&co are the real-time responded rates calculated by the shipping carrier's system based on the parcel size, weight, shipping address, and other options entered. Ultimately, the size and weight measured by the shipping carrier will be applied after your shipment is picked up, therefore, if the size and weight that you entered are different from the actual ones, the estimated rates displayed in Ship&co and the actual billed fee by the carrier will also be different.