Analysis
The effective rate is not flat
A 5% marketplace fee plus a 10% publisher fee is usually summarised as “about 15%”. Plotted against price, the real figure is neither 15% nor constant. At the very bottom of the range it is 66.67% — a one-cent listing costs the buyer $0.03 — and it does not fall below the headline 15% until the buyer price reaches $0.14. Above that it oscillates rather than settling.
Two separate effects
The first is the minimum fee. Each component has a one-cent floor, so on a three-cent listing the buyer pays five cents and two of those cents are fees — 40%, with the percentages playing no part. This effect dies out once the percentage exceeds one cent, at twenty cents of seller proceeds.
The second is independent flooring, and it never dies out. Each fee is rounded down separately, so the discarded fractions reset at different prices. The result is the sawtooth above: 12.28% at fifty cents of proceeds, 13.04% at a dollar, 12.50% at $1.75. The rate is not monotonic, so interpolating between two sampled prices gives an answer that is wrong in between.
| Seller receives | Buyer pays | Total fees | Effective rate |
|---|---|---|---|
| $0.03 | $0.05 | $0.02 | 40.00% |
| $0.05 | $0.07 | $0.02 | 28.57% |
| $0.10 | $0.12 | $0.02 | 16.67% |
| $0.15 | $0.17 | $0.02 | 11.76% |
| $0.20 | $0.23 | $0.03 | 13.04% |
| $0.33 | $0.37 | $0.04 | 10.81% |
| $0.50 | $0.57 | $0.07 | 12.28% |
| $0.75 | $0.85 | $0.10 | 11.76% |
| $1.00 | $1.15 | $0.15 | 13.04% |
| $1.50 | $1.72 | $0.22 | 12.79% |
| $1.75 | $2.00 | $0.25 | 12.50% |
| $2.00 | $2.30 | $0.30 | 13.04% |
| $3.00 | $3.45 | $0.45 | 13.04% |
| $5.00 | $5.75 | $0.75 | 13.04% |
What follows from this
Any estimate of the form “price times 0.85” is wrong at the low end by a wide margin and slightly wrong nearly everywhere else. That matters most for cheap, high-volume items, where a fixed percentage understates the cost of listing by a factor of two or more.
The tabulated form is in the fee lookup table, and how a direct USDT trade works covers the case where the marketplace is bypassed entirely.