Can I refuse a customs charge?

The first thing to establish is which part of the bill you are objecting to, because the two halves behave completely differently.

The government portion — duty plus federal processing fees — is set by statute and regulation. It is not negotiable with the courier, who is simply collecting money it already advanced to CBP on your behalf. If you believe the duty itself is wrong, the route is a correction to the entry, on grounds such as a misclassification or an incorrect declared value. That is a real process with a real remedy, but for a small consumer shipment the effort usually exceeds the amount in dispute.

The carrier portion — advancement, disbursement, brokerage, storage — is set by the carrier's published tariff. That means it is checkable. If a line does not match the published schedule for your shipment date and service, raise it with the carrier's billing team and cite the schedule. This is where disputes are actually won.

Refusing delivery outright is available and sometimes sensible when the charge exceeds what the item is worth. Be aware that the shipment is then returned or abandoned, that some carriers still bill return shipping, and that a refund from the seller is a matter between you and them.