The five lines to add up
Open last month’s settlement statement and look for five things. The sales commission is the obvious one and almost never the largest. The fixed monthly fee, if you pay one, spreads across all your orders, so it hurts more the less you sell.
Then come the three people forget. Shipping: if the marketplace offers the customer free delivery, somebody pays for it, and usually that somebody is you. Promotions: seasonal discounts you join because opting out means disappearing from the listings. And returns, where you often absorb the outbound postage, the inbound postage and the commission on a sale that never happened.
Add the twelve months, divide by what you billed on that channel, and you have your number. It is almost always considerably worse than the advertised rate.
The cost that is not on the statement
There is one line that appears on no document and that, over a couple of years, weighs more than all the others: you do not keep the customer. You do not have their email, you cannot tell them new stock arrived, and if tomorrow the marketplace changes the rules or raises the rate, you have nobody to write to.
That turns a commercial relationship into a dependency. What you are renting is not a shop window; it is your customer list, and the rent goes up when the landlord decides.
Where the lines cross
A proper shop of your own costs €2,500 to €6,000 once in this market, plus maintenance and whatever your payment gateway takes, usually around 1.5%, which does not rise as you grow.
Compare that with your twelve-month number. If what you paid last year in commission clears three thousand euros, the shop pays for itself in year one and year two is clean margin. If you are under a thousand, not yet: stay on the marketplace and do the sum again next year.
And there is a third answer, which is the one we give most often: both. The marketplace to find new customers, your own shop for the ones who come back. The ones who come back are precisely the ones costing you the most commission.