Last November, a seller of health supplements opened his Coupang sales dashboard and found two numbers sitting side by side: ₩98 million in cumulative sales over twelve months, and ₩39.2 million actually deposited into his bank account over the same period. He knew Coupang's commission rate was 10.8%. Ten-point-eight percent of ₩98 million is ₩10.58 million. Until that day, he had no clear idea where the remaining ₩48.22 million had gone.

This piece breaks down that ₩48.22 million.

What the Commission-Rate Table Doesn't Show

The commission rates Coupang publishes by category cover only the fee charged when a sale actually happens. For health supplements, that's 10.8% — a figure printed on the first page of the seller agreement.

But that commission is a cost incurred after the transaction closes. The costs of making the transaction happen in the first place are separate. Break down the cost structure of this seller, who operates through Coupang's Rocket Growth fulfillment program, and the gap becomes visible.

When a customer pays ₩10,000, Coupang doesn't pass that full amount along. It deducts the commission, fulfillment costs, and storage fees first, then settles the remainder. That means ₩1,080 in commission, ₩2,200–2,500 in fulfillment costs (varying with the product's weight and size), and ₩1,500–2,000 in return-processing costs. This seller's return rate ran about 8% — meaning 8 out of every 100 units sold came back.

Once all of that is subtracted, the seller nets an average of ₩6,100–6,300 on a ₩10,000 product. Subtract the ₩3,800 cost of goods, and the profit per unit comes to ₩2,300–2,500. Up to this point, the numbers are roughly predictable — the 10.8% commission plus fulfillment costs. The real problem starts here.

The Invisible Line Item: Advertising

Getting a product seen on Coupang requires advertising. If a listing doesn't reach the top of the search results, sales are unlikely — and that top spot is decided by an auction-based ad system called Coupang Ads.

In the health-supplement category, the average cost per click runs ₩150–300 depending on how competitive the field is. At a typical 3% click-to-purchase conversion rate, generating a single sale takes about 33 clicks — putting the ad spend per sale at ₩4,950–9,900.

This seller's total ad spend over twelve months came to ₩21 million — 21.4% of total revenue.

That's where the math shifts. Add the 21.4% spent on ads to the 10.8% commission, and 32.2% of revenue is already gone. Factor in fulfillment and return-processing costs, and the total share of revenue that ends up flowing back to the Coupang platform reaches 46–51%.

The commission-rate table the platform publishes shows only the first of these line items.

Why Advertising Functions Like a Second Commission

In the second quarter of 2025, the seller tried cutting ad spend by 40%. Sales dropped 31%.

Cut advertising, and visibility drops. Visibility drops, and sales drop. Sales drop, and the listing's ranking on the platform falls. Once ranking falls, advertising has to increase again just to recover. Inside this loop, ad spend isn't a discretionary cost you can dial up or down — it's the price of continuing to sell on the platform at all, and it tends to rise at roughly the same pace as revenue.

Double the sales volume and the commission doubles too. Ad spend, when competition intensifies, tends to more than double. That's why profit doesn't rise in proportion to revenue. The 10.8% commission rate is fixed, but as revenue grows, so does the advertising required just to sustain it.

This was what the seller discovered the first time, twelve months in, that he actually calculated profit and loss by channel: ad spend had been climbing at the same pace as revenue the whole time, and the dashboard never flagged it separately.

What Changed When He Added a Direct Channel

Starting in the second half of 2025, the seller began running his own storefront alongside Coupang — reaching past buyers directly through a KakaoTalk channel and a newsletter.

The shift was modest: over twelve months, direct channels accounted for just 18% of total revenue. But that 18% generated 34% of total profit.

The cost structure was simply different. On the direct channel, the only costs are a roughly 2.5–3% payment-gateway fee, per-order shipping (free above ₩20,000), and the cost of running the KakaoTalk channel. There's no fulfillment fee, and advertising only comes into play when acquiring a new customer. When an existing customer buys again, the ad cost is zero.

The method for pulling existing Coupang customers over to the direct channel was simple: a QR code for a 10% discount on the next purchase, printed inside the shipping box. Roughly one in three led to a KakaoTalk channel follow, and those followers repurchased at 2.3 times the rate of Coupang customers. Every one of those repeat purchases happens without a cent of ad spend.

When he first set up the direct channel, what he was hoping for was revenue diversification. What he actually discovered was how differently the math works out when the same money comes from the same customer through a different channel.

How to Actually Measure Platform Dependence

What this case reveals isn't the size of revenue — it's how profit is distributed across channels.

To see the real numbers, profit has to be attributed by platform. Revenue is easy to split by channel, but profit only becomes accurate once advertising and fulfillment costs are assigned to each channel too. Without that calculation, there's no way to know how far the ₩100 million in headline revenue sits from the actual bottom line.

The ratio of repeat-purchase revenue to ad spend matters just as much. If a customer acquired through a single ad never buys again, that ad cost has to be paid again for every sale. Only a high rate of returning customers brings the per-sale ad cost down over time. When that rate is low, the ad burden grows in step with revenue, no matter how large revenue gets.

The number of customers a seller can reach directly, without going through the platform, needs to be tracked on its own — emails, KakaoTalk channel followers, opt-in text subscribers. Without that number, there's no way to respond when the platform raises its fees or changes its algorithm.

This seller still generates 82% of revenue through Coupang and has no plans to leave. But he says something changed between having no direct channel and having one that accounts for 18%: the feeling, when fees rise, of having absolutely no leverage.