Landed cost includes: product cost, supplier packaging, export fees, freight cost, insurance, import duties, customs clearance fees, port handling, drayage, 3PL receiving fee, and prep cost. Most sellers only count product and freight.
Import duties are often the biggest surprise. Section 301 tariffs on Chinese goods range from 7.5% to 25% of product value depending on HS code. This alone can flip a profitable product into a loss.
Freight cost calculation should use volumetric weight (L x W x H / 5000 in cm) versus actual weight and take the higher value. Light but bulky goods pay by volume, not weight.
Build a full landed cost model before finalizing product sourcing. The product that costs $2 ex-factory but $4 landed is often less attractive than the $3 product that lands at $4.50 from a closer supplier.