We write off what's withheld because fighting it costs more

Each withholding is too small to fight: a contra here, a retention shortfall there, the last application shaved. Individually the economics say let it go, and the economics are right - one at a time. Across a year of jobs, the same sums become a standing discount the business gives to whoever deducts, and the counterparties learn the threshold under which deductions are free.

The fix is to change the economics, not the temperament. Closing accounts run as routine - position stated, records attached, deductions answered in writing while they are fresh - cost little once systematised, and most small withholdings survive on the expectation of silence rather than on merit. Tracked across jobs, the pattern also shows which customers price you down this way, which belongs in the next tender's numbers. Recovered or not, the sums stop being invisible - and deducting stops being free.