110%the most a mover can require at delivery under a non-binding estimate
Under US federal rules, an interstate mover cannot require more than 110% of a non-binding estimate at delivery, or 100% of a binding one, before it unloads your belongings.
FMCSA has a name for movers who hold a loaded truck until you pay more: hostage complaints. It also says a phone rate quote given without inspecting your goods is not an estimate, and paying by card keeps a chargeback available.
Source: Federal Motor Carrier Safety Administration, US Department of Transportation · Federal Motor Carrier Safety Administration, US Department of Transportation. Read more: moving company