Fulfillment choice changes more than shipping cost
WFS and seller fulfillment can have different handling, storage, operational and service implications. Compare the fully loaded cost per order rather than only the outbound shipping charge.
Keep referral fees separate from fulfillment
Marketplace referral economics and fulfillment economics are different cost layers. Modeling them separately makes it easier to see whether a change in fulfillment method actually improves contribution margin.
Include storage and returns
Products with slower turnover, larger dimensions or higher return rates can behave differently from fast-moving compact products. Add storage and return assumptions when comparing scenarios.
Compare at your real order volume
Fixed or monthly operating costs should be allocated across realistic monthly orders. A fulfillment method that wins at high volume may not win at low volume.
Calculate your own numbers
Methodology note: Platform fees and commercial terms can change. Use the linked calculators with the rates and costs that apply to your account and verify current platform documentation before making a business decision.