Almost every "my bill doubled" story traces to one of four causes — extra weight the surveyor never saw, access problems at either end, packing added on moving day, or storage when the delivery slips. All four are manageable in advance and expensive in arrears.
Weight: the estimate was built on a walk-through that missed the garage, the attic, the storage unit. Show the surveyor everything — the embarrassing corners especially — and get a binding estimate in writing.
Access: stairs, elevators, long carries, and streets a 70-foot rig can't enter (a shuttle truck costs real money). Describe both ends honestly at survey time; read our apartment guide if a building is involved.
Packing: "we'll pack ourselves" meets moving-day reality, and crews charge premium rates for rescue packing. Decide honestly, a week early.
Storage-in-transit: the closing slips and your shipment needs somewhere to wait — at a rate you never asked about. Get the SIT rate in the quote even if you're sure you won't need it; our storage guide explains the conversion trap.
Context and measured cost figures for each scenario are in our cost guide, with sources and dates for every number.