Cost the order before you place it, not after
The number a supplier gives you on Alibaba is a price for goods sitting in their factory. Depending on the incoterm it may not include getting the goods onto a ship, and it certainly does not include getting them through customs and into your warehouse. By the time it reaches you the real figure is higher, sometimes dramatically so on low-value high-volume products where freight is a large fraction of goods value.
That gap is where first-time importers get caught. You model your margin on the quoted price, set a retail price off it, place the order, and only discover the true cost when the forwarder's invoice arrives eight weeks later against stock you have already priced. At that point your options are to accept a thinner margin than you planned or to reprice something customers have already seen.
Costing the order first is a twenty minute exercise. Enter the lines the supplier quoted, then add every charge you expect: sea or air freight, duty at your country's rate, customs brokerage, and third-party inspection if you are using it. Ask your forwarder for a freight estimate before you order rather than after, since they will usually give you one against a rough carton count and weight.
Two Alibaba-specific costs deserve their own treatment. Sample fees and tooling or mould charges are real money spent to acquire this product, but they do not belong to any single line on the invoice. Enter them as an other charge and they will be shared across the order, which is the right answer if you are costing this shipment. Bear in mind that a one-off mould charge spread across a first small order will make that order look expensive, and a second order against the same mould genuinely will be cheaper.
The other thing worth checking is what happens at a different order quantity. Suppliers quote lower unit prices at higher MOQs, but freight and duty scale roughly with the order while brokerage and inspection do not. Running the same order at two quantities usually shows the per-unit cost falling faster than the quoted price alone suggests, which is the actual argument for ordering more.