FBA and FBM should be compared using the same selling price and product economics. Comparing one visible fee with one shipping quote is not enough.
Include the complete fulfillment cost
FBA assumptions may include fulfillment, inbound, storage, preparation, and return-related costs. FBM assumptions may include outbound shipping, packaging, handling labor, software, and warehouse or workspace costs.
Consider operational capacity
A lower calculated cost may not be realistic if the seller cannot process orders accurately and on time. Service level and workload are part of the decision.
Test volume changes
The better option can change with order volume, product dimensions, shipping zone, and labor efficiency. Compare at conservative and expected sales levels.
Verify product-specific fees
Fulfillment costs vary by product and can change. Use a current official estimate before making the final decision.