Maker labels that still behave like taker
Post-only intentions fail when the desk’s order type silently removes the maker flag—fee math should follow the fill, not the intention.
Intention and billing diverge. A trader may believe every resting order earns maker rates while the exchange treats certain amend patterns or immediate-or-cancel variants as taker. Spreads that assumed maker-maker suddenly pay taker on one leg.
During fee audits we ask for one recent fill report, not a philosophy of how the desk “usually” works. The fill’s fee line becomes the input. If the desk cannot produce a fill report, we mark the maker assumption as unverified and stress the sheet with taker on the uncertain leg.
That single change has turned more than one “reliable” cross-book route into a break-even exercise. Better to learn it on a worksheet than mid-position.