Short answer
A seller or product page may provide an estimate before the warehouse receives the item. After arrival, the parcel can be measured with packaging, and the shipping line may use actual or volumetric weight. The final route quote should therefore be checked after packing details are known.
How to use this information
Use this answer as a research starting point. Recheck the live platform, seller listing and destination rules before spending money because prices, availability and service terms can change.