Build it up to be checked, not to be trusted

An assessor who has to take your word for a lump sum will discount it; one who can trace every quantity to a drawing and every rate to the pricing document is only checking arithmetic. Lay the build-up out so the reasoning is on the page: quantities, rates, the source of each rate, the logic of any first-principles number. The more your pricing reads like a working rather than a demand, the more of it survives.